A Guide to the National Income and Product Accounts of the United States (NIPA) - (http://www.bea.gov/national/pdf/nipaguid.pdf)
Source: US. Bureau of Economic Analysis
Release: Gross Domestic Product
US. Bureau of Economic Analysis, Real Imports of Goods & Services, 3 Decimal [IMPGSC96], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/IMPGSC96/, September 3, 2015.