DISCLOSURES REGARDING FAIR VALUES OF FINANCIAL INSTRUMENTS - Balance Sheet Location (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Financial assets [Abstract]
Residential mortgage loans	$ 13,958,707	$ 13,908,104
Interest rate swap agreements at fair value	0	1,657
Carrying Amount [Member]
Financial assets [Abstract]
Residential mortgage loans	3,934	4,909
Lending counterparty investments	51,002	5,000
Interest rate swap agreements at fair value	0	1,657
Financial liabilities [Abstract]
Secured borrowings with initial terms of greater than 120 days	3,246,177	2,128,517
Unsecured borrowings	100,000	100,000
Interest rate swap agreements	41,240	27,034
Fair Value [Member]
Financial assets [Abstract]
Residential mortgage loans	4,000	5,000
Lending counterparty investments	51,002	5,000
Interest rate swap agreements at fair value	0	1,657
Financial liabilities [Abstract]
Secured borrowings with initial terms of greater than 120 days	3,248,588	2,128,400
Unsecured borrowings	100,300	100,500
Interest rate swap agreements	$ 41,240	$ 27,034
Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Repurchase arrangements with initial terms	120 days