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Investment Securities Available For Sale - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,980,415	$ 1,534,389
Unrealized Gains	35,721	17,989
Unrealized Losses	(9,996)	(40,126)
Fair Value	$ 2,006,140	$ 1,512,252
Agency ARMs
Debt Securities, Available-for-sale [Line Items]
Weighted average reset period	26 months	31 months
Agency RMBS:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 922,976	$ 1,076,006
Unrealized Gains	7,410	8
Unrealized Losses	(7,509)	(38,284)
Fair Value	922,877	1,037,730
Unrealized gains (losses), net	(100)
Agency RMBS: | Unrealized gains (losses) , net
Debt Securities, Available-for-sale [Line Items]
Fair Value	21,000
Agency RMBS: | Agency ARMs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	55,740	73,949
Unrealized Gains	13	8
Unrealized Losses	(1,347)	(2,563)
Fair Value	54,406	71,394
Agency RMBS: | Agency Fixed-Rate
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	867,236	1,002,057
Unrealized Gains	7,397	0
Unrealized Losses	(6,162)	(35,721)
Fair Value	868,471	966,336
Agency CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	51,334	0
Unrealized Gains	19	0
Unrealized Losses	(395)	0
Fair Value	50,958	0
Unrealized gains (losses), net	(400)
Agency CMBS | Unrealized gains (losses) , net
Debt Securities, Available-for-sale [Line Items]
Fair Value	30,700
Total Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	974,310	1,076,006
Unrealized Gains	7,429	8
Unrealized Losses	(7,904)	(38,284)
Fair Value	973,835	1,037,730
Non-Agency RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	701,583	215,337
Unrealized Gains	14,992	166
Unrealized Losses	(1,261)	(1,466)
Fair Value	715,314	214,037
Unrealized gains (losses), net	1,200
Non-Agency RMBS | Unrealized gains (losses) , net
Debt Securities, Available-for-sale [Line Items]
Fair Value	123,800
CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	254,620	243,046
Unrealized Gains	13,300	17,815
Unrealized Losses	(143)	(376)
Fair Value	267,777	260,485
Unrealized gains (losses), net	500
Investment securities held in securitization		52,700
CMBS | Unrealized gains (losses) , net
Debt Securities, Available-for-sale [Line Items]
Fair Value	20,600
ABS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	49,902	0
Unrealized Gains	0	0
Unrealized Losses	(688)	0
Fair Value	49,214	$ 0
Unrealized gains (losses), net	(700)
ABS | Unrealized gains (losses) , net
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 49,200

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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