You are given a text that consists of multiple sentences. Your task is to perform abstractive summarization on this text. Use your understanding of the content to express the main ideas and crucial details in a shorter, coherent, and natural sounding text. 
Text: In 2020, we had a terrific year despite an extremely challenging operating environment.
We delivered extraordinary results through disciplined execution and resilience.
I am extremely proud of our EMCOR team.
I don't think any of us could have imagined this high level of performance when we started to understand the impact of COVID-19 on our operations in March of 2020.
In 2020, we had $8.8 billion in revenues and set records on an adjusted basis for earnings per diluted share of $6.40, operating income of $490 million and operating income margin of 5.6%.
We also had record operating cash flow of $806 million.
Mark's going to cover all the financials in much more detail and especially the key components of our cash flow performance in his financial commentary, inclusive of the fourth quarter and full year 2020 performance.
We delivered these stellar results because we have diversity and demand for our services.
And we have end markets that have proved resilient and have provided us with opportunities to execute well for our customers.
These results are a testament to our skilled employees and our subsidiary, segment and corporate leadership, who kept focused and resolute through the ever-changing environment in 2020.
Across our company, we worked hard to keep our employees safe, and it was our number one priority throughout the year.
We innovated and found ways to maintain and even improve our productivity.
We became leaner and even more expeditious in our decision-making.
And we're able to leverage technology to connect our leadership effectively to the front lines despite COVID-19 protocols.
We did not let obstacles become excuses.
Instead, we overcame obstacles, and we delivered exceptional results.
I now want to highlight some of our segment performance.
Our Electrical Construction segment performed well with 8.4% operating income margins.
Despite the disruptions in some of our operations from COVID-19 and due to shutdowns, we still posted outstanding results.
These results were driven by excellent execution in the commercial sector driven by data center and telecommunication and really excellent execution across all market sectors.
We've performed the work well and really innovated on the means, the methods and the scheduling so that we can not only keep our employees safe, but enhance our productivity.
Our Mechanical Construction segment had an exceptional year by any measure.
We also had 8.4% operating income margins with exceptional performance across the commercial sector, again driven by telecommunications and data centers.
And we also had strength in warehousing, manufacturing, water and wastewater and the healthcare end markets.
We showed great innovation through increased use of BIM or building information modeling and prefabrication and worked hard to keep our employees safe and productive.
We believe in both of our construction segments that we not only met, but we exceeded our customers' expectations.
Our United States Building Services segment team showed grit and resilience as they faced the COVID-19 disruption in late March, April and May, with many of our customer sites not acceptable, bookings off as much as 40% in some of our subsidiary companies and in some of our product lines and a very cautious resumption of decision-making by our customers to allow us to resume service and projects.
We did rebound robustly from mid-June forward, and we're well prepared to execute project work for our customers that optimize their equipment and control systems, improve the wellness of their facilities through indoor air quality or IAQ solutions and sought to help our customers return to work safely and productively.
We also served as the boots on the ground for our customers to keep lightly occupied buildings, campuses and schools operational, functioning and safe over the past 10 months.
We are well positioned to keep serving our customers as they reopen and seek to make their building safe, efficient and productive for their employees.
Our U.K. Building Services segment mirrored the performance of our U.S. Building Services segment.
We navigated the severe lockdown actions in the U.K. and continued to keep our customers productive, operational and able to conduct their businesses.
We also made organizational changes that enhanced our leaders' responsiveness by making our organization even flatter, more aligned and leaner, which has led to crisper and more efficient decision-making.
Our U.K. team continues to win in the market as we have a culture of innovation and execution.
As you all know, our Industrial Services segment mostly serves the downstream oil and gas or refining and petrochemical markets.
These end markets had a severe dislocation of demand as planes stop flying and people stop driving.
And this segment was also impacted at the beginning of the year with a disruption in the global oil and gas markets.
We cut costs aggressively and maintain profitability on an EBITDA basis.
We are well positioned with demand for our services returns, which is not likely to happen until the fourth quarter of this year.
We expect the larger, more sophisticated, well-capitalized service providers to emerge stronger.
And yes, we are clearly one of them.
We exit 2020 with our remaining performance obligations or RPOs at an all-time high of $4.6 billion, 13.8% higher than the year-ago period.
We have very strong RPOs and are continuing to benefit from the very strong demand for data center construction, logistics and supply chain support, especially with our fire protection trade, healthcare, water and wastewater.
And we expect manufacturing to be as strong also as 2021 progresses.
We expect to benefit from increasing demand for IAQ, that's indoor air quality, and building efficiency projects and solutions.
We depart 2020 with an exceptional balance sheet that allows us the room to grow and build for the future while continuing to return cash to our shareholders through dividends and share repurchases.
2020 was an extraordinary year, and we performed exceptionally well, which is a real testament to our people, our subsidiary leaders, our segment staff and leadership and our corporate staff and leadership.
I will now turn the discussion over to Mark.
Over the next several slides, I will provide a detailed discussion of our fourth quarter results before moving to our full year performance, some of which Tony outlined during his opening commentary.
So let's discuss EMCOR's fourth quarter performance.
Consolidated revenues of $2.3 billion in quarter four are down $122.4 million or 5.1% from 2019.
Our fourth quarter results include $55.4 million of revenues attributable to businesses acquired pertaining to the period of time that such businesses were not owned by EMCOR in last year's fourth quarter.
Acquisition revenues positively impacted both our United States Mechanical Construction and United States Building Services segments.
Excluding the impact of businesses acquired, fourth quarter 2020 consolidated revenues decreased $177.9 million or 7.4% organically.
Our segment performance was mixed within the quarter, with most of our reportable segments experiencing quarter-over-quarter organic revenue declines.
In general, we have seen reductions in revenues in those geographies or market sectors which are continuing to be most significantly impacted by the COVID-19 pandemic.
However, when we consider the incremental revenue generated from our acquisitions, we were successful in generating fourth quarter revenue growth from three of our five reportable segments.
Specific segment revenue performance for the quarter is as follows: United States Electrical Construction segment revenues of $493.5 million decreased $71 million or 12.6% from quarter four 2019.
Revenues declined across multiple market sectors due to the continuing impact of the COVID-19 pandemic, including the associated containment and mitigation measures as well as the curtailment of capital spending by some of our customers.
Consistent with my third quarter commentary, this segment experienced a significant reduction in revenues from industrial project work within the manufacturing market sector, where certain of our electrical businesses perform services for both midstream and upstream oil and gas customers.
Additionally, the segment's operations that serve the metropolitan New York and California markets continue to face revenue headwinds as these geographies remain some of the most restrictive with regards to COVID protocols.
United States Mechanical Construction segment revenues of $969.4 million increased $73.8 million or 8.2% from quarter four 2019.
Excluding acquisition revenues of $24.2 million, the segment's revenues increased $49.6 million or 5.5% organically.
Revenue growth within the quarter was broad based across most market sectors, with commercial and healthcare representing the most significant period-over-period increases.
These revenue gains were partially offset by a quarterly revenue decline in manufacturing market sector activity due to the completion or substantial completion of certain large projects during the early part of 2020.
This revenue performance represents an all-time quarterly record for our United States Mechanical Construction segment and surpasses the previous record set in 2019's fourth quarter.
EMCOR's total domestic construction business fourth quarter revenues of $1.46 billion increased $2.7 million or less than 0.25%.
United States Building Services revenues of $568.1 million increased $29.1 million or 5.4%.
However, when excluding acquisition revenues of $31.2 million, this segment's quarterly revenues decreased $2.1 million or 40 basis points.
Revenue gains within their mobile mechanical services division resulting from incremental contribution from acquired companies and their commercial site-based services division due to new contract awards or scope expansion on certain existing contracts were partially offset by a quarter-over-quarter revenue decline within the segment's energy services division due to reduced large project activity when compared to 2019's fourth quarter.
Consistent with our United States Mechanical Construction Services segment, revenue performance within our United States Building Services segment represents an all-time quarterly record.
United States Industrial Services revenues of $135.5 million decreased by $163.7 million or 54.7% as this segment continues to be impacted by the negative macroeconomic conditions and uncertainty within the markets in which it operates.
Cost control and cash preservation actions taken by customers of this segment have resulted in the suspension of capital spending programs and the curtailment of maintenance activity, which has severely impacted demand for our Industrial Service offerings.
With the rise in telecommuting and the various restrictions on travel in response to COVID-19, there have been significant reductions in both vehicle miles driven and airline miles traveled, which is further prolonging the weakened demand this segment has been experiencing since late quarter one of 2020.
United Kingdom Building Services segment revenues of $115 million increased $9.4 million or 8.9% from last year's quarter.
Revenue gains for the quarter resulted from strong project activity as well as incremental revenue from new contract awards.
Additionally, fourth quarter 2020 revenues were positively impacted by $2.9 million as a result of favorable foreign exchange rate movement in the period.
Selling, general and administrative expenses of $244.6 million reflects an increase of $3.7 million from quarter four 2019.
The current period includes approximately $4.4 million of incremental expenses from businesses acquired, inclusive of intangible asset amortization, resulting in an organic quarter-over-quarter decrease of approximately $700,000.
A reduction in salaries expense due to a decrease in head count necessitated by lower organic revenue as well as reduced travel and entertainment expenses due to a combination of cost-avoidance measures as well as restricted company travel were the primary reasons for the organic decline in SG&A.
These decreases were largely offset by an increase in quarterly incentive compensation expense due to EMCOR's actual operating performance exceeding its previously forecasted 2020 full year results.
As a percentage of revenues, selling, general and administrative expenses totaled 10.7% in quarter four 2020 versus 10% in the year-ago period.
The quarter-over-quarter increase can be attributed to the reduction in our consolidated quarterly revenues without a commensurate decrease in certain of our fixed overhead costs, including those of our Industrial Services segment as we do not deem the current operating environment to be permanent.
Our assessment continues to be based on our evaluation of future market opportunities.
And we expect to see some return to normalcy in industrial maintenance and capital spending when we ultimately move beyond the depressed demand caused by the COVID-19 pandemic.
Reported operating income for the quarter of $137.6 million represents a $14.7 million or 12% increase when compared to operating income of $122.9 million in last year's fourth quarter.
This operating income performance eclipses our previously established all-time quarterly record, which was achieved in 2020's third quarter.
Our fourth quarter operating margin was 6%, which compares favorably to the 5.1% of operating margin reported in 2019's fourth quarter.
We experienced the operating margin expansion within each of our reportable segments other than our U.S. Industrial Services segment, which is reporting an operating loss for the fourth quarter and our U.K. Building Services segment, which achieved a consistent margin in each year's quarterly period.
Specific quarterly performance by reportable segment is as follows: our United States Electrical Construction segment had operating income of $43.4 million, which increased by $2.1 million from the comparable 2019 period.
Reported quarterly operating margin is 8.8% and represents a 150 basis point improvement over 2019's fourth quarter.
This increase in both operating income dollars and operating margin is largely attributable to increased gross profit contribution from commercial market sector activities, inclusive of numerous telecommunications construction projects.
These gross profit gains were partially offset by reduced gross profit contribution from the transportation and manufacturing market sectors due to both the closeout of projects in prior periods as well as the continued headwinds attributable to the COVID-19 pandemic.
Fourth quarter operating income of the United States Mechanical Construction Services segment of $100.4 million represents a $31.5 million increase from last year's quarter, while operating margin in the quarter of 10.4% represents a 270 basis point improvement over 2019.
This segment has continued to experience strength in the majority of the market sectors we serve, most notably demonstrated by increased gross profit contribution from project activity in the commercial, healthcare and institutional market sectors.
In addition, our Mechanical Construction segment experienced a more favorable mix of work than in the prior year and benefited from strong performance by our fire protection operations.
Our combined U.S. construction business is reporting a 9.8% operating margin and $143.7 million of operating income, which has increased from 2019's fourth quarter by $33.5 million or 30.4%.
Operating income for United States Building Services of $28 million represents a $3.8 million increase from last year's fourth quarter, and operating margin of 4.9% represents an improvement of 40 basis points when compared to the prior year.
This segment experienced improved gross profit performance from its mobile mechanical services division, inclusive of incremental contribution from acquired companies.
In addition, the segment continues to benefit from reduced levels of selling, general and administrative expenses due to cost-mitigation actions implemented in response to the COVID-19 pandemic.
Our United States Industrial Services segment operating loss of $8.2 million represents a decline of $21.3 million, which compares to operating income of $13.1 million in last year's fourth quarter.
These conditions have resulted in considerable reductions in capital spending by certain of our customers, which has led to a decrease in demand for this segment's service offerings.
This environment was further exacerbated by an active hurricane season, which resulted in the suspension of planned maintenance activities that would have occurred during both quarters three and four of 2020.
United Kingdom Building Services operating income of $4.2 million represents an increase of approximately $300,000 over quarter four of 2019.
Operating margin was 3.7% for both quarter periods.
We are now on slide nine.
Additional financial items of significance for the quarter not previously addressed are as follows: quarter four gross profit of $383.9 million or 16.8% of revenues is improved over last year's quarter by $19.1 million and 160 basis points of gross margin.
Restructuring expenses in 2020's fourth quarter pertain to the realignment of management resources within our combined U.S. construction operations.
Diluted earnings per common share of $1.45 compares to $1.54 per diluted share in last year's fourth quarter.
Adjusting our 2020 quarterly performance for the negative impact on our income tax rate resulting from the nondeductible portion of the noncash impairment charges recording -- recorded during the second quarter of 2020, non-GAAP diluted earnings per share for the quarter ended December 31, 2020, is $1.86, which favorably compares to last year's fourth quarter by $0.32 or nearly 21%.
Our tax rate for quarter four of 2020 is 41.8%, which is significantly higher than the tax rate for the corresponding 2019 period due to the nondeductibility of the majority of the impairment charges just referenced.
My last comment on slide nine is with respect to our $259.5 million of operating cash flow in the quarter, which favorably compares to $178.8 million of operating cash flow in the year-ago period and reflects the continued effective management of working capital by our subsidiary leadership teams.
Our operating cash flow was aided by the organic decline in revenues, which resulted in a contraction in accounts receivable.
Additionally, the deferral of the employer's portion of social security taxes in the United States benefited our cash flow by approximately $35.2 million during the fourth quarter of 2020.
On a full year basis, the social security tax deferrals, coupled with the deferral of value-added tax in the United Kingdom, has favorably impacted our 12-month operating cash flow by approximately $117.3 million.
These amounts will be repaid in 2021 and 2022.
And obviously, we'll have the opposite effect on our operating cash flow in such future periods.
With the fourth quarter commentary complete, I will now augment Tony's introductory remarks on EMCOR's annual performance.
Consolidated revenues of $8.8 billion represent a decrease of $377.6 million or 4.1% when compared to our record annual revenues in 2019 of $9.17 billion.
Our year-to-date results include $269.6 million of revenues attributable to businesses acquired pertaining to the period of time that such businesses were not owned by EMCOR in the 2019 period.
Acquisitions positively impacted each of our United States Electrical Construction, United States Mechanical Construction and the United States Building Services segments.
Excluding the impact of businesses acquired, year-to-date revenues decreased organically 7.1%, primarily as a result of the significant revenue contraction experienced during quarter two as the majority of our operations were most significantly impacted by the COVID-19 pandemic during such period.
In addition, our annual revenues were negatively impacted by a decrease in demand for certain of our service offerings within our United States Electrical Construction services and United States Industrial Services segments as a result of the adverse conditions experienced within the oil and gas industry.
Discrete segment revenue performance for full year 2020 is as follows: United States Electrical Construction segment revenues of $1.97 billion decreased $243.2 million or 11% from 2019's $2.22 billion of revenues; acquisitions contributed $25.4 million of incremental revenues, resulting in an organic decline of $268.5 million or 12.1%.
Revenue contraction within the majority of the market sectors in which we operate.
Most notably, the commercial and manufacturing market sectors were the primary drivers of this year's year-over-year decrease.
As I mentioned in my commentary on our fourth quarter results, although this segment has a diverse geographic footprint, a number of its operating companies within both the metropolitan New York and California markets were severely impacted by COVID protocols, which resulted in a decrease in the number of short-duration project opportunities as well as various project delays.
These impacts, coupled with the completion or substantial completion of certain large projects in 2019, contributed to the decline in organic annual revenues.
In addition, and as previously referenced, certain of our operations in the segment which are exposed to the upstream and midstream oil and gas sector experienced a significant decline in demand in 2020.
Partially offsetting these revenue reductions were increased revenues from project activities within the institutional and hospitality market sectors during the year.
United States Mechanical Construction revenues of $3.49 billion increased $145.2 million or 4.3% compared to 2019.
Acquisitions contributed $188.8 million of incremental revenues to the segment, which, when excluded, results in an organic revenue decline of $43.7 million or 1.3% from 2020.
This organic decrease can be largely attributed to reduced project volume within the manufacturing market sector with a heavy concentration in the food processing submarket sector as a result of the completion or substantial completion of certain large projects in 2019.
Similar to our United States Electrical Construction segment, this segment additionally experienced the negative effects of the COVID-19 pandemic, which resulted in a reduced number of short-duration project opportunities during calendar 2020.
United States Building Services segment revenues of $2.11 billion increased $3.2 million or less than 0.5%.
Acquisitions contributed $55.4 million of revenues, resulting in an organic revenue decline of 2.5% when compared to full year 2019.
The decrease in project and building controls activities within the segment's mobile mechanical services division, largely as a result of the impact of the COVID-19 pandemic, which resulted in the temporary closure of certain customers' facilities, coupled with the decrease in large project activity within the segment's energy services division were the primary contributors to such organic revenue reduction.
In addition, the segment experienced a decrease in revenues from its government services division as a result of the loss of certain contracts not renewed pursuant to rebid.
These revenue contractions were partially offset by increased customer demand for certain services aimed at improving the indoor air quality within their facilities as well as an increase in revenues within the segment's commercial site-based services division as a result of new contract awards and scope expansion on certain existing contracts.
United States Industrial Services segment revenues of $797.5 million decreased $290.1 million or 26.7% from 2019's $1.09 billion of revenues.
At the risk of sounding repetitive, for most of 2020, the segment has been severely impacted by negative conditions and uncertainty within the markets in which it operates due to the dislocation between crude oil supply and demand resulting from COVID-19 and geopolitical tensions within OPEC.
In addition, during the back half of 2020, the segment experienced suspension and deferral maintenance in capital projects by its customers as a result of hurricane and tropical storm activity in the United States Gulf Coast region.
Revenues of our United Kingdom Building Services segment for 2020 increased 1.7% to $430.6 million, primarily as a result of new maintenance contract awards within the commercial and institutional market sectors.
Revenues were also favorably impacted by $2.3 million as a result of exchange rate movement in the pound sterling year-over-year.
Selling, general and administrative expenses of $903.6 million represent 10.3% of revenues as compared to $893.5 million or 9.7% of revenues in 2019.
Full year 2020 SG&A includes $29.6 million of incremental expenses, inclusive of intangible asset amortization pertaining to businesses acquired.
Excluding such incremental amounts, our SG&A has decreased $19.4 million on an organic basis, primarily as a result of certain cost reductions resulting from our actions taken in response to the COVID-19 pandemic.
As referenced during my quarter commentary, the increase in SG&A as a percentage of revenues is a result of the organic decrease in our revenue without a commensurate decrease in certain of our fixed overhead costs as we do not deem the current operating environment to be permanent.
2020's year-to-date operating income is $256.8 million.
Adjusting this amount to exclude the noncash impairment loss on goodwill, identifiable intangible assets and other long-lived assets recorded in the second quarter, our non-GAAP operating income for the year was $489.6 million.
This compares to operating income of $460.9 million for full year 2019 and represents a $28.7 million or 6.2% improvement year-over-year.
Despite the headwinds experienced in 2020, three of our five reportable segments achieved higher operating income and higher operating margins than that of the prior year.
Of the two segments which did not, United States Building Services is reporting a modest decline of just over 1%, while our United States Industrial Services segment suffered a significant year-over-year reduction, resulting in an operating loss for 2020.
With regard to each segment's discrete performance, I will start with our electrical -- United States Electrical Construction segment.
Their 2020 operating income of $166.5 million represents an all-time segment record, and it is an increase of $4.8 million or 3% compared to the prior year.
Operating margin for 2020 is 8.4%, which is 110 basis points higher than 2019.
This year-over-year improvement in operating income dollars was due to a reduction in selling, general and administrative expenses due to cost-control measures enacted during the course of 2020.
The increase in operating margin for the year was a result of an increase in gross profit margin given favorable project execution and a more profitable mix of work within this segment.
These improvements in gross profit margin were partially offset by an increase in the ratio of selling, general and administrative expenses to revenues as a result of the year-over-year revenue contraction within the Electrical Construction segment.
United States Mechanical Construction operating income of $292.5 million increased $67.5 million or 30% over 2019 levels, and operating margin reached 8.4% versus 6.7% in the prior year.
Acquired companies contributed incremental operating income of $9.3 million, inclusive of $12.7 million of amortization expense associated with identifiable intangible assets.
The increase in operating income for 2020 was primarily due to strong project performance throughout the year in the majority of the market sector served by this segment, resulting in an increase in annual gross profit.
The 170 basis point improvement in operating margin was also a result of our solid project execution and improved gross profit margin, most notably within the manufacturing and commercial market sectors.
These increases in gross profit and gross profit margin were partially offset by an increase in selling, general and administrative expenses, primarily as a result of an increase in incentive compensation expense due to the improved year-over-year operating performance for this segment.
United States Building Services operating income for 2020 of $113.4 million declined by $1.3 million or 1.2% due to a reduction in year-over-year large project activity within the segment's energy services division as well as decreased project and building control opportunities within their mechanical services division due to both temporary closure and restricted access to certain customer facilities impacted by the COVID-19 pandemic.
These reductions were partially offset by incremental operating income contribution from companies acquired, which totaled $4.5 million, inclusive of $3.2 million of amortization expense associated with identifiable intangible assets.
In addition, this segment experienced increased gross profit resulting from greater demand for certain services aimed at improving indoor air quality as various customers made changes to their HVAC systems in advance of their employees returning to work as recommended by the Center for Disease Control.
Operating margin of 5.4% was consistent with the prior year as a reduction in gross profit margin was offset by a decrease in the ratio of selling, general and administrative expenses to revenues due to certain cost-reduction measures taken during 2020.
Our United States Industrial Services segment incurred an operating loss of $2.8 million for 2020 as compared to operating income of $44.3 million in 2019.
This segment implemented significant cost reductions during the year in an effort to mute the year-over-year decline.
However, as previously discussed, this segment's overhead structure includes a significant investment in fixed infrastructure, including plant and equipment.
As we view current market conditions to be -- as to be temporary, that infrastructure is needed to respond to changes in demand patterns once they ultimately recover.
Operating income of our United Kingdom Building Services segment of $20.7 million or 4.8% of revenues compares to operating income of $18.3 million or 4.3% of revenues in the prior year.
The $2.3 million improvement is largely due to an increase in gross profit from new maintenance contract awards, while the 50 basis point expansion in operating margin is attributable to both the increase in gross profit margin as well as a reduction in the ratio of selling and general and administrative expenses to revenues.
SG&A of this segment benefited from various cost-control initiatives implemented by our U.K. team.
We are now on slide 12.
Additional key financial data on slide 12 not addressed during my full year commentary is as follows: year-to-date gross profit of $1.4 billion is greater than 2019's gross profit by $39.5 million, while gross margin of 15.9% is higher than last year's 14.8% by 110 basis points.
Total restructuring costs of $2.2 million are increased from 2019 due to actions taken during 2020 to both realign certain management functions as well as rightsize our cost structure in light of the revenue headwinds we faced.
Diluted earnings per common share was $2.40 compared to $5.75 per diluted share a year ago.
When adjusting this amount for the impact of the noncash impairment charges recorded in 2020 second quarter, non-GAAP diluted earnings per share of $6.40 as compared to the same $5.75 in last year's annual period.
This represents a $0.65 or 11.3% improvement year-over-year.
We are now on slide 13.
As outlined on this slide, EMCOR's liquidity profile remains strong despite the headwinds we faced during the course of 2020.
Our cash balance has increased from $358.8 million at December 31, 2019, to $902.9 million at the end of 2020.
Operating cash flow of $806.4 million, aided by the FICA and VAT cash tax deferrals previously referenced, was the primary driver of this increase.
Operating cash flow was partially offset by cash used in investing activities of nearly $95 million, predominantly representing payments for acquisitions of businesses and capital expenditures as well as cash used in financing activities, which totaled $172 million and consisted of the repurchase of our common stock, net repayments under our credit facility and dividends paid to our stockholders.
Working capital has increased by over $236 million as a result of the increase in our cash balance, partially offset by a reduction in accounts receivable given the lower organic revenue during the period as well as an increase in contract liabilities due to advanced billing on certain long-term construction projects.
Other changes in key balance sheet positions of note are as follows: goodwill has decreased since December 31, 2019, as a result of the noncash impairment charge recognized during the second quarter of 2020, partially offset by an increase in goodwill resulting from businesses acquired or purchase price adjustments made during the year.
Our identifiable intangible asset balance has decreased since the end of last year largely due to $60 million of amortization expense recorded during 2020, which was partially offset by incremental intangible assets recognized as a result of the acquisition of three businesses during calendar 2020.
Total debt has decreased by $35.7 million since the end of 2019, reflecting our net financing activity during the year.
And course, debt-to-capitalization ratio has decreased to 11.9% from 13.2% in the year-ago period.
Lastly, our stockholders' equity has decreased slightly since December 2019 as our net income was offset by share repurchases, dividend payments and postretirement plan liability adjustments made during 2020.
Our balance sheet, in conjunction with the credit available to us, continues to put us in a position to invest in our business and achieve our strategic objectives as we look forward to 2021 and years beyond that.
Hey, Mark, that's a well-deserved drink of water.
And year-end was always the toughest and we've been doing it a long time together.
Remaining performance obligation or RPO by segment and market sector.
I'll go through the numbers briefly and then go deeper to the market trends we are seeing.
As I stated in my remarks, total RPOs at the end of 2020 were a shade under $4.6 billion, up $559 million or 13.8% when compared to the year-ago level of $4.03 billion.
The strength of our RPO and the associated bidding activities surprised us a bit given the uncertainty of the pandemic, economic dislocation and disruptions for the year.
However, as we have said in the past, during uncertain and challenging times, we have often seen a flight to quality and fiscally strong construction and service providers prosper.
It's still a little too early to tell by 2020 and now into 2021.
It sure looked like one of those times.
I should probably repeat.
My mic wasn't on.
So I'm going to go on to page 14, remaining performance obligations by segment and market sector.
Look, they're up $559 million or 13.8% for those that didn't hear it.
And really, there's a flight to quality a lot of times when you move from 2020 into 2021, and this certainly looks like one of those times.
Our domestic construction segments experienced strong project growth in 2020 with RPOs increasing $495 million or 15.2% since the end of 2019 as we continue -- and continue to see demand for electrical mechanical systems, both in new construction and retrofit projects.
Our United States Building Services segment RPOs increased in the quarter as this segment's small project repair service work continue to rebound from its abrupt, almost hard stop at the beginning and the height of COVID-19.
Some of this resumption is a return of regularly scheduled maintenance on mechanical systems and then the return of small project work.
And some is focused, as you'd imagine, around modifications and improvements in IAQ, indoor air quality, which I will discuss in detail in a few slides.
It was quite a recovery from the March, April and May time frame when the segment was hit especially hard as described earlier, with bookings down 40% in many cases.
Over on the right side of the page, we show RPOs by market sector.
Throughout 2020, we experienced strong year-over-year growth in the commercial, healthcare and water and wastewater sectors.
Commercial projects, which make up 41% of that total RPOs, increased $297 million or close to 19% for the year.
As we stated last quarter and continued to experience in the fourth quarter of this year, demand for hyper data -- scale data center construction has high demand, as does high-tech manufacturing, and warehousing and logistics also remain strong.
We are a nationwide leader in this section of the commercial market sector, and quite frankly, I don't see any letup in this activity anytime soon.
We are also in Part one design discussion on several large design build through process opportunities.
For the year, healthcare project RPOs increased $207 million or 56%.
And water and wastewater project RPOs grew similar by 57% to $173 million.
As one might surmise, given the impact of the pandemic, healthcare as a sector of the nonresidential construction market is expected to be slightly higher in 2021 and likely better than that for us as our customers build new facilities and retrofit existing facilities.
By the way, RPOs in these three market sectors are at all-time highs for us since we transitioned to RPO reporting from backlog reporting in March of 2018.
The nonresidential market, as measured by the U.S. Census Bureau for put-in-place activity, remains a very large market, and it was roughly $800 billion at the end of December 31, 2020.
It's down 5% in 2020.
However, it is not a uniform market, given its size and breadth and opportunities still exist.
On the next page, I will discuss how well-thought and patient capital allocation strategy has allowed this growth in our RPO base and growth to occur despite choppy and uncertain overall markets.
And on nonresidential market, they decreased 5%.
I'm now on page 15, capital allocation.
We have long had a major market presence in mechanical and electrical construction services and have continued to allocate capital to fill in the white space, either geographically or by adding capability in these important segments.
Further, we have used our capital to build leading capabilities in HVAC service, building controls and mechanical system retrofit.
We have built that capability and capacity through organic growth and acquisition in a sustained manner over many years.
We are also one of the country's leading life safety contractors.
And this activity mostly resides in our mechanical, and that is the sprinkler fitters and electrical, fire alarm and security installation and upgrades and low-voltage systems construction segments.
Again, these capabilities were built over a long period of time through acquisition and organic investment.
These are concrete examples where we have built successful platforms that allow us to have the capability to serve a broad spectrum of customers with the right products and specialty trade capabilities.
Our investment decisions and patience have allowed us to build and maintain capability through cycles and serve a diverse set of customer opportunities.
We have not only invested in over 20 acquisitions and we spent around $555 million on those acquisitions since 2017 until today, but we also have returned significant cash to our shareholders through share repurchases and dividends.
I'm now on page 16, titled Resilient Markets.
As we discussed on the previous two pages, we have shown that we have very good diversity of demand at EMCOR, and we have used that capital to grow organically and through acquisition to allow us to build upon such diversity of demand and resiliency in our business.
This is not an accident, but it is a part of our long-term capital allocation strategy as discussed on the previous page.
For example, EMCOR's data center capabilities were built enhanced over a very long period of time.
We started building the largest data centers in the country for financial institutions and the original hosting providers almost 20 years ago.
Today, we build data centers that are five times larger to seven times larger than these previous "large data centers".
We have continued to grow that capability over the last five years and expanded through organic investment or acquisition or a combination of both.
We are one of the leaders in the specialty contracting for these complex facilities.
That's all the electrical trades, mechanical trades and sprinkler fitters.
Data center construction is a good market for us, and we expect it to be for the foreseeable future.
It is also a growing part of our maintenance activities.
We have -- we are fortunate to have other markets that have shown resiliency.
We continue to support our customers' e-commerce growth primarily through our life safety services and the construction of large cold storage and other warehouse facilities as our customers transform their warehouse networks to allow for more fast-paced growth.
We continue to believe that we are very well positioned to support our customers as they build more resiliency into their supply chains by reshoring projects.
We also continue to see significant opportunity for large and small design-build food processing clients.
Health care is also a good market for us and has been for a very long period of time.
These are complex facilities that are seeking to become more flexible in the delivery of their care in the long term.
Water and wastewater is a market that we believe will have significant opportunity for us and has significant opportunity for us today and also in the next three to five years, especially in Florida.
And finally, as I have discussed previously, is our position as a leading HVAC services contractor.
We are in a compelling position to provide indoor air quality solutions and services.
We see very strong demand currently and expect this to continue over many years.
We have experienced and are continuing to experience strong demand for upgrading, enhancing HVAC and building control systems for both energy efficiency and flexibility of demand and use.
This has always been a good market for EMCOR for many years, and it spans all market sectors.
As discussed, serving these resilience markets is not by chance.
We've built this capability over many years, and we have some of the best field leadership, trade supervision and skilled trades people in the industry to execute in these markets.
I'm now going to wrap this up on page 17 and 18.
As we enter 2021, we are still in the world of COVID-19 mitigation and restriction.
The oil and gas markets are still depressed, and the nonresidential market is expected to decline by another 3% to 5%.
Despite that less-than-cheery backdrop, we expect to continue to perform well in 2020.
We expect revenues of $9.2 billion to $9.4 billion and expect to earn $6.20 to $6.70 in earnings per diluted share.
2021 should be another year of outstanding performance.
We will have to execute very well to maintain the 2020 record levels of operating income margins of 8.4% in our Electrical and Mechanical Construction segments.
We do expect to increase revenues, which may help us mitigate this challenge.
Underlying this range are the following assumptions: our Industrial Services segment does not materially improve until the fourth quarter but gain strong momentum headed into 2020 as demand for refined products will continue to be challenged during 2021, especially through the end of the second quarter.
The nonresidential construction market will decline modestly.
We will continue to execute well in our more resilient rock market sectors to include manufacturing, commercial driven by data centers and logistics and warehousing, water and wastewater, energy retrofits and healthcare.
Our end market diversity has been and continues to be a real strength of EMCOR.
We do not expect a more restrictive COVID-19 environment than what we are operating in today.
We do expect a more normal pre-COVID-19 operating environment to emerge as the year progresses.
We are operating near 100% capability on our jobs with no meaningful COVID-19-induced issues.
Our leadership and trades people have learned how to work and even prosper under the COVID precautions.
We have learned to plan and execute, but always have the mindset that our employee safety comes first, which is nothing new or novel for us as it is one of our core values.
We expect to continue to help our customers improve their facilities' air quality with indoor air quality solutions, improve energy efficiency through replacement projects and optimizing their systems.
And we are going to help them bring back their employees back to work with an improved piece of mind through our efforts.
Our ability to move to the upper range of our earnings guidance range will depend on the following: the nonresidential market, especially our more resilient markets, are stronger than projected because the bounce back is faster as the U.S. and the U.K. normalizes from COVID-19 restrictions.
Our refining and petrochemical customers begin to gain more comfort with improved demand for rerefined products and increase their scope for this year's work performed by us.
Our momentum in indoor air quality and efficiency projects continues to not only increase but accelerates further, and our productivity stays strong as we transition to more normal operating conditions.
I'm going to talk a little bit about what happened in Texas last week as we have a significant business in Texas.
Clearly, the power disruption in Texas last week affected not only EMCOR's business operations, customer sites, but also more importantly, our employees and their families.
Many of our customers went to skeleton staff for three to five days, and many shut down operations almost completely.
We have mostly resumed operations in our Industrial Services and also our construction services and Building Service customer sites.
We will be there to help our customers complete their planned turnarounds, execute on planned maintenance and repairs related to the storm and to resume project work already under way or that was ready to start in the last few weeks.
We have may -- we may have work that was planned for the first quarter that will now extend into the second quarter that -- and it may have had more activity in the first quarter than it will now have.
We expect to continue to be balanced capital allocators as we have shown on the previous pages.
We have more capital to allocate in balance, but we know how to do that.
And however, our guidance contemplates that we will continue to be disciplined allocators between organic growth investments, acquisitions, share repurchases and dividends.

user
q4 earnings per share $1.45.
q4 revenue $2.28 billion versus refinitiv ibes estimate of $2.2 billion.
sees fy 2021 earnings per share $6.20 to $6.70.
q4 non-gaap earnings per share $1.86.
sees fy 2021 revenue $9.2 billion to $9.4 billion.

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