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Investment Securities Available for Sale, at Fair Value - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Schedule of Investments [Line Items]
Contractual maturities (up to)	40 years
Weighted average life of available for sale securities portfolio	7 years 4 months 24 days	5 years
Allowance for credit loss	$ 0
Gross unrealized losses	(117,011,000)		$ (124,000)
Other-than-temporary impairment recorded in earnings		$ 0
Non-Agency RMBS
Schedule of Investments [Line Items]
Gross unrealized losses	(102,709,000)		0
CMBS
Schedule of Investments [Line Items]
Gross unrealized losses	$ (14,302,000)		$ (124,000)

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Amount of allowance for credit loss 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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of other-than-temporary impairment (OTTI) on investment in debt security, recognized in earnings.

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