Input Impedance of Noninverting Amplifier
When you buy an op-amp (or model it) you get a bit more than most folk bargain for. This picture is just showing the input terminal stuff: -



Here we have: -


Input bias current and its friend; input offset current
Various input resistances (differential and common mode)
Input offset voltage (and its drift with temperature)
Various differential and common mode capacitances
Input noise voltage (usually specified as a density)
Input noise current (usually specified as a density)


Added to this is: -


Limited common mode input voltage range.
Finite common mode rejection that usually gets a lot worse at higher frequencies.
Bias current roughly doubling for every 10 degC rise (FET input devices).
Power supply rejection - noise on the power supply WILL modify the output voltage and it gets worse at higher frequencies.


And there are several non-input related limitations such as: -


Restricted ability to get close to either power rail.
Limited slew rate (the output cannot move faster than "so-many" volts per micro second).
Open-loop Gain falling from a finite (but usually very high value) to unity at some point (commonly between 1 MHz and 10 MHz but there will be exceptions).
Small signal output overshoot.
Inability of output to drive more than a few tens of mA.
Less than ideal phase margin (can lead to a linear amplifier becoming an oscillator especially with capacitive loads on the output).
Non-perfect channel-to-channel seperation i.e. cross-talk in multiple op-amp packages.
Output voltage phase reversal (due to extreme input voltages).