The Publication Manual of the American Psychological Association does not have a separate format for government documents. They should be cited the same way as books, articles, web sources, brochures, etc.
Many government documents are technical or research reports. Examples of how to cite those documents can be found below.
Author's Last Name, Author's Initials. (Year). Title of work (Report No. 123). Location: Publisher.
If the report was retrieved online, omit Location: Publisher, and include the publisher/agency in the retrieval statement:
Author's Last Name, Author's Initials. (Year). Title of work (Report No. 123). Retrieved from Agency name: http://www.address.gov
Name of Agency, Subdivision of Agency. (Date). Title of work (Report No. 123). Retrieved from Agency Name website: http://www.address.gov
United States Department of Commerce, United States Census Bureau. (2015, October 2). A snapshot of monthly manufacturing statistics in the United States (MFG15-M3). Retrieved from the United States Census Bureau website: http://www.census.gov/content/dam/Census/library/publications/2015/econ/mfg15-m3.pdf