DISCLOSURES REGARDING FAIR VALUES OF FINANCIAL INSTRUMENTS - Fair Value and Related Disclosures for Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Agency Securities Classified as Available-for-sale [Member] | Fannie Mae/Freddie Mac [Member]
Available-for-sale securities disclosure Items [Abstract]
Available-for-sale securities, Amortized Cost Basis	$ 10,345,542	$ 10,559,231
Available-for-sale securities, Gross Unrealized Gains	218,095	243,351
Available-for-sale securities, Gross Unrealized Losses	601	2,218
Available-for-sale securities, Fair Value	10,563,036	10,800,364
Agency Securities Classified as Available-for-sale [Member] | Ginnie Mae [Member]
Available-for-sale securities disclosure Items [Abstract]
Available-for-sale securities, Amortized Cost Basis	3,377,433	3,087,570
Available-for-sale securities, Gross Unrealized Gains	16,278	16,755
Available-for-sale securities, Gross Unrealized Losses	4,811	5,157
Available-for-sale securities, Fair Value	3,388,900	3,099,168
Residential Mortgage Securities Classified as Held-to-Maturity [Member]
Held-to-maturity securities disclosure [Abstract]
Held-to-maturities, Amortized Cost Basis	2,837	3,663
Held-to-maturities, Gross Unrealized Gains	53	124
Held-to-maturities, Gross Unrealized Losses	0	0
Held-to-maturities, Fair Value	$ 2,890	$ 3,787