Source: US. Bureau of Economic Analysis
Release: Gross Domestic Product
A Guide to the National Income and Product Accounts of the United States (NIPA) - (http://www.bea.gov/national/pdf/nipaguid.pdf)
US. Bureau of Economic Analysis, Real Imports of Goods and Services, 3 Decimal [IMPGSC96], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/IMPGSC96, July 23, 2016.