Securities - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2013	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, allowance for credit loss	$ 0			$ 0
Available-for-sale securities transferred to held-to-maturity securities			$ 536,000,000.0
Unrealized net loss on securities transferred from available-for-sale to held-to-maturity, gross			$ 13,300,000
Realized gain or losses on the sale of available-for-sale securities	0	$ 0
Corporate debt securities, callable, amortized cost	54,300,000
Corporate debt securities, callable, estimated fair value	54,000,000.0
Securities pledged for other debt obligations, at fair value	533,000,000.0			435,900,000
Equity investments, at estimated fair value	50,159,000			107,079,000
Reverse Repurchase Agreement
Debt Securities, Available-for-sale [Line Items]
Securities pledged for repurchase agreements, at fair value	147,000,000.0			$ 152,700,000
CLOs
Debt Securities, Available-for-sale [Line Items]
Corporate debt securities, callable, amortized cost	96,400,000
Corporate debt securities, callable, estimated fair value	$ 96,500,000