Investment Securities Available For Sale - Available-For-Sale Securities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,534,389	$ 1,417,724
Unrealized Gains	17,989	21,031
Unrealized Losses	(40,126)	(25,674)
Fair Value	1,512,252	1,413,081
Proceeds from sale of investment securities available-for-sale	26,900	107,100	$ 208,200
Realized net loss from sale of investment securities	12,300	100	$ 2,300
Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Investment securities held in securitization	52,700	47,922
Total Agency ARMs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	73,949	93,331
Unrealized Gains	8	22
Unrealized Losses	(2,563)	(2,281)
Fair Value	71,394	91,072
Total Agency Fixed Rate
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,002,057	1,059,532
Unrealized Gains	0	669
Unrealized Losses	(35,721)	(12,916)
Fair Value	966,336	1,047,285
Total Agency IOs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0	41,367
Unrealized Gains	0	271
Unrealized Losses	0	(10,459)
Fair Value	0	31,179
Total Agency RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,076,006	1,194,230
Unrealized Gains	8	962
Unrealized Losses	(38,284)	(25,656)
Fair Value	1,037,730	1,169,536
Non-Agency RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	215,337	100,291
Unrealized Gains	166	1,852
Unrealized Losses	(1,466)	(18)
Fair Value	214,037	102,125
CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	243,046	123,203
Unrealized Gains	17,815	18,217
Unrealized Losses	(376)	0
Fair Value	260,485	141,420
CMBS \| Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Investment securities held in securitization	52,700	47,900
Freddie Mac \| Total Agency ARMs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	26,338	33,623
Unrealized Gains	0	16
Unrealized Losses	(1,052)	(852)
Fair Value	25,286	32,787
Freddie Mac \| Total Agency Fixed Rate
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	87,018	20,804
Unrealized Gains	0	0
Unrealized Losses	(2,526)	(736)
Fair Value	84,492	20,068
Freddie Mac \| Total Agency IOs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0	8,436
Unrealized Gains	0	19
Unrealized Losses	0	(2,756)
Fair Value	0	5,699
Fannie Mae \| Total Agency ARMs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	43,984	54,958
Unrealized Gains	8	6
Unrealized Losses	(1,384)	(1,236)
Fair Value	42,608	53,728
Fannie Mae \| Total Agency Fixed Rate
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	915,039	1,038,363
Unrealized Gains	0	669
Unrealized Losses	(33,195)	(12,174)
Fair Value	881,844	1,026,858
Fannie Mae \| Total Agency IOs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0	11,310
Unrealized Gains	0	22
Unrealized Losses	0	(2,989)
Fair Value	0	8,343
Ginnie Mae \| Total Agency ARMs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,627	4,750
Unrealized Gains	0	0
Unrealized Losses	(127)	(193)
Fair Value	3,500	4,557
Ginnie Mae \| Total Agency Fixed Rate
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0	365
Unrealized Gains	0	0
Unrealized Losses	0	(6)
Fair Value	0	359
Ginnie Mae \| Total Agency IOs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0	21,621
Unrealized Gains	0	230
Unrealized Losses	0	(4,714)
Fair Value	$ 0	$ 17,137

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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