Investment Securities - Narrative (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) security	Dec. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($)	Dec. 31, 2012 shares
Debt Securities, Available-for-sale [Line Items]
Cost of third party management	$ 900,000	$ 800,000	$ 1,500,000
Number of securities with unrealized losses | security	1	2
SEREF
Debt Securities, Available-for-sale [Line Items]
Number of shares acquired (in shares) | shares				9,140,000
Equity security, fair value	$ 11,600,000	$ 11,200,000
Ownership percentage	2.00%
VIE eliminations
Debt Securities, Available-for-sale [Line Items]
Fair value of investment securities before consolidation of VIEs eliminated against VIE liabilities	$ 22,200,000
Fair value option
Debt Securities, Available-for-sale [Line Items]
Fair value of mortgage backed securities	1,500,000,000
RMBS
Debt Securities, Available-for-sale [Line Items]
Portion of securities with variable rate	$ 126,400,000
RMBS | Available-for-sale
Debt Securities, Available-for-sale [Line Items]
Portion of securities with variable rate (as a percent)	88.00%
RMBS | Fair value option
Debt Securities, Available-for-sale [Line Items]
Portion of securities with variable rate	$ 0
Fair value of investment securities before consolidation of VIEs	250,400,000
Unpaid principal balance of investment securities before consolidation of VIEs	127,400,000
CMBS | Fair value option
Debt Securities, Available-for-sale [Line Items]
Portion of securities with variable rate	98,200,000
Fair value of investment securities before consolidation of VIEs	1,300,000,000
Unpaid principal balance of investment securities before consolidation of VIEs	$ 2,800,000,000