Investment Securities Available for Sale - Schedule of Available for Sale Securities (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	$ 1,882,843	$ 1,534,389
Unrealized Gains	30,505	17,989
Unrealized Losses	(9,330)	(40,126)
Fair Value	1,904,018	1,512,252
Agency ARMs
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	60,135	73,949
Unrealized Gains	17	8
Unrealized Losses	(1,481)	(2,563)
Fair Value	$ 58,671	71,394
Weighted average reset period	27 years
Agency ARMs \| Freddie Mac
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	$ 23,841	26,338
Unrealized Gains	0	0
Unrealized Losses	(675)	(1,052)
Fair Value	23,166	25,286
Agency ARMs \| Fannie Mae
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	33,323	43,984
Unrealized Gains	17	8
Unrealized Losses	(705)	(1,384)
Fair Value	32,635	42,608
Agency ARMs \| Ginnie Mae
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	2,971	3,627
Unrealized Gains	0	0
Unrealized Losses	(101)	(127)
Fair Value	2,870	3,500
Agency Fixed- Rate
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	898,806	1,002,057
Unrealized Gains	4,857	0
Unrealized Losses	(6,496)	(35,721)
Fair Value	897,167	966,336
Agency Fixed- Rate \| Freddie Mac
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	79,266	87,018
Unrealized Gains	997	0
Unrealized Losses	(433)	(2,526)
Fair Value	79,830	84,492
Agency Fixed- Rate \| Fannie Mae
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	819,540	915,039
Unrealized Gains	3,860	0
Unrealized Losses	(6,063)	(33,195)
Fair Value	817,337	881,844
Agency RMBS
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	958,941	1,076,006
Unrealized Gains	4,874	8
Unrealized Losses	(7,977)	(38,284)
Fair Value	955,838	1,037,730
Non-Agency RMBS
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	610,624	215,337
Unrealized Gains	11,800	166
Unrealized Losses	(896)	(1,466)
Fair Value	$ 621,528	214,037
Weighted average reset period	45 years
CMBS
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	$ 264,721	243,046
Unrealized Gains	13,831	17,815
Unrealized Losses	(154)	(376)
Fair Value	$ 278,398	260,485
Weighted average reset period	1 month
CMBS \| Available-for-sale securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Investment securities, available for sale held in securitization trusts		52,700
ABS
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	$ 48,557	0
Unrealized Gains	0	0
Unrealized Losses	(303)	0
Fair Value	$ 48,254	$ 0

Debt Securities, Available-for-sale, Weighted Average Reset Period

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The total amount of cash and securities held by third party trustees pursuant to terms of debt instruments or other agreements as of the date of each statement of financial position presented, which can be used by the trustee only to pay the noncurrent portion of specified obligations.

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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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Amount, before tax, of unrealized loss 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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Amortized cost of 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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