RESIDENTIAL INVESTMENT SECURITIES - Weighted Average Life (Details) - Residential Investments - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Estimated Fair Value
Less than one year	$ 10,123	$ 471,977
Greater than one year through five years	12,523,917	13,838,890
Greater than five years through ten years	76,865,618	77,273,833
Greater than ten years	874,724	716,121
Total	90,274,382	92,300,821
Amortized Cost
Less than one year	10,159	476,538
Greater than one year through five years	12,774,529	13,925,749
Greater than five years through ten years	79,772,617	78,431,852
Greater than ten years	887,580	708,363
Total	$ 93,444,885	$ 93,542,502