XML 58 R46.htm IDEA: XBRL DOCUMENT v3.7.0.1
Mortgage-Backed and Credit Risk Transfer Securities - Fair Value of Mortgage-Backed Securities According to Weighted Average Life Classification (Detail) - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]    
Less than one year $ 109,860 $ 121,076
Greater than one year and less than five years 6,842,335 6,719,923
Greater than or equal to five years 8,968,902 8,140,332
Fair value $ 15,921,097 $ 14,981,331