1. A computer-implemented method comprising: parsing, by a server computing device, each document of a corpus of documents to determine phrases found in each of the documents; analyzing, by the server computing device, each determined phrase with respect to each document to determine a frequency of occurrence of the phrase in the document relative to a frequency of occurrence of the phrase in the corpus; identifying, by the server computing device, documents that comprise a same statistically improbable phrase, wherein the statistically improbably phrase is one of the determined phrases having both of: a probability of occurrence in a document of the corpus of documents that is higher than probability of occurrence of other phrases in the document; and a probability of occurrence in the corpus of documents that is lower than probability of occurrence of other phrases in the corpus of documents; and grouping, by the server computing device, the identified documents that comprise the statistically improbable phrase into a single group of documents.