Investment Securities - AFS and Fair Value Option (Details) $ in Thousands	Jun. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($)
RMBS
Unrealized Losses
Portion of securities with variable rate	$ 170,500
RMBS \| Available-for-sale
Estimated Fair Value
Securities with a loss less than 12 months	2,118	$ 2,148
Unrealized Losses
Securities with a loss less than 12 months	$ (22)	(31)
Number of securities with unrealized loss position \| security	1
Portion of securities with variable rate		$ 177,400
RMBS \| Fair value option
Unrealized Losses
Fair value of investment securities before consolidation of VIEs	$ 63,200
Unpaid principal balance of investment securities before consolidation of VIEs	34,900
Portion of securities with variable rate	0
CMBS \| Fair value option
Unrealized Losses
Fair value of investment securities before consolidation of VIEs	1,200,000
Unpaid principal balance of investment securities before consolidation of VIEs	2,900,000
Portion of securities with variable rate	145,000
VIE eliminations
Unrealized Losses
Fair value of investment securities before consolidation of VIEs eliminated against VIE liabilities	$ 44,700

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Represents the fair value balance of the investment securities before consolidation of the VIEs.

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Represents the unpaid principal balance of the investment securities before consolidation of the VIEs.

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Represents the amount of investment securities bearing variable interest rates.

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Amount of 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 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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Number of investments in debt securities 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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