Investment Securities Available for Sale - Schedule of Available for Sale Securities (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	$ 1,732,866	$ 1,534,389
Unrealized Gains	21,769	17,989
Unrealized Losses	(10,766)	(40,126)
Fair Value	1,743,869	1,512,252
Agency ARMs
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	64,230	73,949
Unrealized Gains	20	8
Unrealized Losses	(1,731)	(2,563)
Fair Value	$ 62,519	71,394
Weighted average reset period	28 months
Agency ARMs \| Freddie Mac
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	$ 24,618	26,338
Unrealized Gains	0	0
Unrealized Losses	(733)	(1,052)
Fair Value	23,885	25,286
Agency ARMs \| Fannie Mae
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	36,379	43,984
Unrealized Gains	20	8
Unrealized Losses	(895)	(1,384)
Fair Value	35,504	42,608
Agency ARMs \| Ginnie Mae
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	3,233	3,627
Unrealized Gains	0	0
Unrealized Losses	(103)	(127)
Fair Value	3,130	3,500
Agency Fixed- Rate
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	938,478	1,002,057
Unrealized Gains	1,730	0
Unrealized Losses	(8,527)	(35,721)
Fair Value	931,681	966,336
Agency Fixed- Rate \| Freddie Mac
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	82,165	87,018
Unrealized Gains	650	0
Unrealized Losses	(502)	(2,526)
Fair Value	82,313	84,492
Agency Fixed- Rate \| Fannie Mae
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	856,313	915,039
Unrealized Gains	1,080	0
Unrealized Losses	(8,025)	(33,195)
Fair Value	849,368	881,844
Agency RMBS
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	1,002,708	1,076,006
Unrealized Gains	1,750	8
Unrealized Losses	(10,258)	(38,284)
Fair Value	994,200	1,037,730
Non-Agency RMBS
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	428,443	215,337
Unrealized Gains	4,719	166
Unrealized Losses	(322)	(1,466)
Fair Value	$ 432,840	214,037
Weighted average reset period	5 months
Purchases not yet settled included in accrued expenses and other liabiiities	$ 3,100
CMBS
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	276,947	243,046
Unrealized Gains	15,300	17,815
Unrealized Losses	(157)	(376)
Fair Value	$ 292,090	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	$ 24,768	0
Unrealized Gains	0	0
Unrealized Losses	(29)	0
Fair Value	$ 24,739	$ 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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Amount of expenses incurred but not yet paid classified as other.

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