Author, A. A. (Year). Title of work (Report No. xxx). Retrieved from URL
Author, A. A. (Year). Title of work (Report No. xxx). Washington, DC: U.S. Government Printing Office.
U.S. Department of Commerce, Census Bureau. (2015, July 16). Who Votes? Congressional Elections and the American Electorate: 1978-2014 (Report No. P20-577). Retrieved from http://www.census.gov/content/dam/Census/library/publications/2015/demo/...
In-text: (U.S. Department of Commerce, 2015, p. 4)
Include the agency name in the retrieval statement if the agency that published the report is not already identified in the author field (i.e. Retrieved from U.S. Census Bureau website: URL).