Residential Investment Securities - Weighted Average Life (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value of Agency Mortgage-Backed Securities according to their estimated weighted-average life:
Less than one year	$ 83,514	$ 37,862
Greater than one year through five years	53,216,416	20,278,111
Greater than five years through ten years	13,272,846	46,473,701
Greater than ten years	8,086	443,820
Total	66,580,862	67,233,494
Amortized Cost of Agency Mortgage-Backed Securities according to their estimated weighted-average life:
Less than one year	84,500	37,850
Greater than one year through five years	52,372,346	20,066,435
Greater than five years through ten years	13,163,536	47,174,319
Greater than ten years	8,071	436,693
Total	$ 65,628,453	$ 67,715,297