Context is a set of grouping of reported facts that all share the same reporting period or segment information.

However, some filers have been submitting facts within a context that do not share the same reporting period as the context. As illustrated below, if the context date is June 30, 2017, then all dates that fall within that context must also be June 30, 2017, such as the Document Period End Date. The only exceptions are Entity Common Stock, Shares Outstanding or Entity Public Float as the dates for these elements usually are filing submission dates. ¹ 

For more information on context date, see EDGAR Filer Manual 6.5.19.