Investments (Additional Information) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2020 USD ($)	Dec. 31, 2017 USD ($)
Schedule of Investments [Line Items]
Net unrealized gain on available-for-sale securities, net of tax	$ 29,310	$ 3,250	$ (17,826)		$ (10,300)
Deferred Tax Liabilities, Investments	$ 8,000
Deferred Tax Assets, Unrealized Losses on Available-for-Sale Securities, Gross		890,000,000
Unrealized Loss as a Percent of Amortized Cost	1.00%
Security Owned And Pledged As Collateral Amortized Cost	$ 485,000	709,000
Security Owned and Pledged as Collateral, Fair Value	507,100	712,400
Trading securities	4,161	3,799
Debt Securities, Available-for-sale, Allowance for Credit Loss	0			$ 0
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 0
Number of Holdings, HTM Investments in Unrealized Loss Positions | security	0
Debt Securities, Held-to-Maturity, Excluded Accrued Interest from Amortized Cost	$ 10	10
Proceeds from Sale of Other Investments	1,700
Equity Securities, FV-NI, Realized Gain (Loss)	1,200
Marketable Securities, Realized Gain (Loss)	$ 38
Marketable Securities, Unrealized Gain (Loss)		$ 928	$ (50)