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Investment Securities Available for Sale - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Schedule of Investments [Line Items]
Proceeds from sales of investment securities	$ 41,200,000		$ 98,000,000.0	$ 26,900,000
Realized net gain (loss) on sales of investment securities available for sale	5,000,000.0		$ 21,800,000	(12,300,000)
Contractual maturities (up to)			41 years
Weighted average life of available for sale securities portfolio			5 years 7 months 6 days		5 years 8 months 12 days
Gross unrealized losses	(8,323,000)		$ (8,323,000)		$ (40,126,000)
Other-than-temporary impairment recorded in earnings	0	$ 0	0	$ 0
Agency RMBS
Schedule of Investments [Line Items]
Gross unrealized losses	(7,977,000)		(7,977,000)		(38,284,000)
Non-Agency RMBS
Schedule of Investments [Line Items]
Gross unrealized losses	(192,000)		(192,000)		(1,466,000)
CMBS
Schedule of Investments [Line Items]
Gross unrealized losses	$ (154,000)		$ (154,000)		$ (376,000)

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Amount of realized gain (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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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 unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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