1. A method, performed by at least one computer system, of retrieving documents in response to a search query submitted on a first date that includes one or more phrases, the method comprising: selecting from a corpus of documents a plurality of documents that include at least one of the one or more phrases and that are relevant to the query based on a relevance score for the selected documents; determining, using a processor of the at least one computer system, for at least one of the selected 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 selected documents, the weighted relevance score for a particular document being based on the relevance score for the particular document and a difference between the first date and the date range for the particular document; and ranking, using a processor of the at least one computer system, the selected documents according to their weighted relevance scores.