DISCLOSURES REGARDING FAIR VALUES OF FINANCIAL INSTRUMENTS - Fair Value and Related Disclosures for Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Residential Mortgage Securities Classified as Held-to-Maturity [Member]
Held-to-maturity securities disclosure [Abstract]
Held-to-maturities, Amortized Cost Basis	$ 1,837	$ 2,037
Held-to-maturities, Gross Unrealized Gains	19	24
Held-to-maturities, Fair Value	1,856	2,061
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	10,681,367	10,372,566
Available-for-sale securities, Gross Unrealized Gains	102,336	134,797
Available-for-sale securities, Gross Unrealized Losses	12,561	23,990
Available-for-sale securities, Fair Value	10,771,142	10,483,373
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	2,829,057	2,833,460
Available-for-sale securities, Gross Unrealized Gains	10,234	10,141
Available-for-sale securities, Gross Unrealized Losses	8,870	15,313
Available-for-sale securities, Fair Value	$ 2,830,421	$ 2,828,288

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Name Accounting Standards Codification
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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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