1. A method, performed by at least one computer system, of retrieving documents in response to a search query that includes a phrase and a first date, the method comprising: selecting, from a corpus of documents, a plurality of documents that are relevant to the query; determining, using a processor of the at least one computer system, for at least one of the plurality of documents, a date range for the document, the date range representing a period for which no change in the document has been detected; calculating, using a processor of the at least one computer system, a weighted relevance score for each of the plurality of documents, the weighted relevance score for a particular document being a relevance score for the particular document adjusted by a difference between the first date and the date range for the particular document when the particular document has a date range; and ranking, using a processor of the at least one computer system, the plurality of documents according to their weighted relevance scores.