DISCLOSURES REGARDING FAIR VALUES OF FINANCIAL INSTRUMENTS - Fair Value and Related Disclosures for Debt Securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Residential Mortgage Securities Classified as held-to-Maturity [Member]
Held-to-maturity securities disclosure [Abstract]
Held-to-maturities, Amortized Cost Basis	$ 3,304	$ 3,663
Held-to-maturities, Gross Unrealized Gains	98	124
Held-to-maturities, Gross Unrealized Losses	0	0
Held-to-maturities, Fair Value	3,402	3,787
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	10,715,709	10,559,231
Available-for-sale securities, Gross Unrealized Gains	243,152	243,351
Available-for-sale securities, Gross Unrealized Losses	559	2,218
Available-for-sale securities, Fair Value	10,958,302	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	3,167,628	3,087,570
Available-for-sale securities, Gross Unrealized Gains	20,148	16,755
Available-for-sale securities, Gross Unrealized Losses	3,903	5,157
Available-for-sale securities, Fair Value	$ 3,183,873	$ 3,099,168

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Fair value of investments in debt securities classified as held-to-maturity.

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