SEGMENT REPORTING - Schedule of Segments (Details) - USD ($) $ in Thousands				3 Months Ended			9 Months Ended
		May 01, 2019	Feb. 06, 2019	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Income Statement [Abstract]
Interest income				$ 82,251		$ 90,386	$ 254,040	$ 253,822
Interest expense				(51,397)		(51,476)	(155,015)	(144,606)
Net interest income				30,854		38,910	99,025	109,216
Provision for loan losses				0		(10,300)	(600)	(13,600)
Net interest income after provision for loan losses				30,854		28,610	98,425	95,616
Operating lease income		$ 3,900		24,405			81,106
Operating lease income						24,997		79,306
Sale of loans, net				11,247		1,861	38,589	12,893
Realized gain (loss) on securities				3,396		(2,554)	10,726	(4,896)
Unrealized gain (loss) on equity securities				254		0	1,341	0
Unrealized gain (loss) on Agency interest-only securities				16		142	38	456
Realized gain (loss) on sale of real estate, net				2,082		63,704	963	96,341
Impairment of real estate				0	$ (1,400)	0	(1,350)	0
Fee and other income				5,166		4,851	17,047	17,579
Net result from derivative transactions				(9,465)		7,115	(35,956)	29,156
Earnings (loss) from investment in unconsolidated joint ventures				1,094		401	3,617	466
Gain (loss) on extinguishment/defeasance of debt			$ (1,100)	0		(4,323)	(1,070)	(4,392)
Total other income (loss)				38,195		96,194	115,051	226,909
Salaries and employee benefits				(14,319)		(15,792)	(52,800)	(46,754)
Operating expenses				(5,314)		(5,464)	(16,727)	(16,608)
Real estate operating expenses				(6,270)		(7,152)	(17,776)	(23,806)
Fee expense				(2,056)		(1,311)	(4,951)	(2,953)
Depreciation and amortization		$ (400)		(9,030)		(10,417)	(29,192)	(31,896)
Total costs and expenses				(36,989)		(40,136)	(121,446)	(122,017)
Income tax (expense) benefit				(1,112)		(1,204)	(478)	(5,679)
Net income (loss)				30,948		83,464	91,552	194,829
Total assets	[1]			6,619,874			6,619,874		$ 6,272,872
Investment in unconsolidated joint ventures	[1]			51,419			51,419		40,354
Investment in FHLB stock	[1]			61,619			61,619		57,915
Professional fees				3,000		2,900	9,100	8,700
Operating Segment
Income Statement [Abstract]
Investment in unconsolidated joint ventures				51,400			51,400		40,400
Operating Segment | Loans
Income Statement [Abstract]
Interest income				66,422		81,779	209,369	228,273
Interest expense				(12,063)		(17,232)	(41,043)	(46,286)
Net interest income				54,359		64,547	168,326	181,987
Provision for loan losses				0		(10,300)	(600)	(13,600)
Net interest income after provision for loan losses				54,359		54,247	167,726	168,387
Operating lease income				0			0
Operating lease income						0		0
Sale of loans, net				11,247		1,861	38,589	12,893
Realized gain (loss) on securities				0		0	0	0
Unrealized gain (loss) on equity securities				0			0
Unrealized gain (loss) on Agency interest-only securities				0		0	0	0
Realized gain (loss) on sale of real estate, net				0		0	0	0
Impairment of real estate							0
Fee and other income				3,839		3,895	13,095	10,823
Net result from derivative transactions				(6,557)		3,741	(20,273)	14,516
Earnings (loss) from investment in unconsolidated joint ventures				0		0	0	0
Gain (loss) on extinguishment/defeasance of debt						0	0	(69)
Total other income (loss)				8,529		9,497	31,411	38,163
Salaries and employee benefits				0		0	0	0
Operating expenses				0		61	0	61
Real estate operating expenses				0		0	0	0
Fee expense				(1,264)		(928)	(3,516)	(2,160)
Depreciation and amortization				0		0	0	0
Total costs and expenses				(1,264)		(867)	(3,516)	(2,099)
Income tax (expense) benefit				0		0	0	0
Net income (loss)				61,624		62,877	195,621	204,451
Total assets				3,387,157			3,387,157		3,482,929
Operating Segment | Securities
Income Statement [Abstract]
Interest income				15,515		8,541	43,844	25,217
Interest expense				(5,632)		(1,482)	(12,250)	(3,423)
Net interest income				9,883		7,059	31,594	21,794
Provision for loan losses				0		0	0	0
Net interest income after provision for loan losses				9,883		7,059	31,594	21,794
Operating lease income				0			0
Operating lease income						0		0
Sale of loans, net				0		0	0	0
Realized gain (loss) on securities				3,396		(2,554)	10,726	(4,896)
Unrealized gain (loss) on equity securities				254			1,341
Unrealized gain (loss) on Agency interest-only securities				16		142	38	456
Realized gain (loss) on sale of real estate, net				0		0	0	0
Impairment of real estate							0
Fee and other income				428		0	1,165	72
Net result from derivative transactions				(2,908)		3,374	(15,683)	14,640
Earnings (loss) from investment in unconsolidated joint ventures				0		0	0	0
Gain (loss) on extinguishment/defeasance of debt						0	0	0
Total other income (loss)				1,186		962	(2,413)	10,272
Salaries and employee benefits				0		0	0	0
Operating expenses				0		0	0	0
Real estate operating expenses				0		0	0	0
Fee expense				(92)		(91)	(280)	(297)
Depreciation and amortization				0		0	0	0
Total costs and expenses				(92)		(91)	(280)	(297)
Income tax (expense) benefit				0		0	0	0
Net income (loss)				10,977		7,930	28,901	31,769
Total assets				1,911,456			1,911,456		1,410,126
Operating Segment | Real Estate
Income Statement [Abstract]
Interest income				7		6	21	16
Interest expense				(9,646)		(9,213)	(27,620)	(25,799)
Net interest income				(9,639)		(9,207)	(27,599)	(25,783)
Provision for loan losses				0		0	0	0
Net interest income after provision for loan losses				(9,639)		(9,207)	(27,599)	(25,783)
Operating lease income				24,405			81,106
Operating lease income						24,997		79,306
Sale of loans, net				0		0	0	0
Realized gain (loss) on securities				0		0	0	0
Unrealized gain (loss) on equity securities				0			0
Unrealized gain (loss) on Agency interest-only securities				0		0	0	0
Realized gain (loss) on sale of real estate, net				2,082		63,704	963	96,341
Impairment of real estate							(1,350)
Fee and other income				0		0	7	3,416
Net result from derivative transactions				0		0	0	0
Earnings (loss) from investment in unconsolidated joint ventures				1,094		401	3,617	466
Gain (loss) on extinguishment/defeasance of debt						(4,323)	(1,070)	(4,323)
Total other income (loss)				27,581		84,779	83,273	175,206
Salaries and employee benefits				0		0	0	0
Operating expenses				0		0	0	0
Real estate operating expenses				(6,270)		(7,152)	(17,776)	(23,806)
Fee expense				(700)		(292)	(1,155)	(496)
Depreciation and amortization				(9,005)		(10,398)	(29,118)	(31,840)
Total costs and expenses				(15,975)		(17,842)	(48,049)	(56,142)
Income tax (expense) benefit				0		0	0	0
Net income (loss)				1,967		57,730	7,625	93,281
Total assets				1,032,752			1,032,752		1,038,376
Corporate/Other
Income Statement [Abstract]
Interest income				307		60	806	316
Interest expense				(24,056)		(23,549)	(74,102)	(69,098)
Net interest income				(23,749)		(23,489)	(73,296)	(68,782)
Provision for loan losses				0		0	0	0
Net interest income after provision for loan losses				(23,749)		(23,489)	(73,296)	(68,782)
Operating lease income				0			0
Operating lease income						0		0
Sale of loans, net				0		0	0	0
Realized gain (loss) on securities				0		0	0	0
Unrealized gain (loss) on equity securities				0			0
Unrealized gain (loss) on Agency interest-only securities				0		0	0	0
Realized gain (loss) on sale of real estate, net				0		0	0	0
Impairment of real estate							0
Fee and other income				899		956	2,780	3,268
Net result from derivative transactions				0		0	0	0
Earnings (loss) from investment in unconsolidated joint ventures				0		0	0	0
Gain (loss) on extinguishment/defeasance of debt						0	0	0
Total other income (loss)				899		956	2,780	3,268
Salaries and employee benefits				(14,319)		(15,792)	(52,800)	(46,754)
Operating expenses				(5,314)		(5,525)	(16,727)	(16,669)
Real estate operating expenses				0		0
Fee expense				0		0	0	0
Depreciation and amortization				(25)		(19)	(74)	(56)
Total costs and expenses				(19,658)		(21,336)	(69,601)	(63,479)
Income tax (expense) benefit				(1,112)		(1,204)	(478)	(5,679)
Net income (loss)				(43,620)		$ (45,073)	(140,595)	$ (134,672)
Total assets				288,509			288,509		341,441
Investment in FHLB stock				61,600			61,600		57,900
Deferred tax (liability)				(4,700)			(4,700)
Deferred tax asset									2,300
Corporate/Other | Senior Unsecured Notes
Income Statement [Abstract]
Senior notes				$ 1,200,000			$ 1,200,000		$ 1,200,000

[1] Includes amounts relating to consolidated variable interest entities. See Note 10.