Investments (Additional Information) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Net unrealized gains (losses) on available-for-sale securities, net of tax	$ 3,250,000	$ (17,826,000)	$ (10,300,000)	$ (6,085,000)
Deferred Tax Liabilities, Investments	$ 890,000,000
Deferred Tax Assets, Unrealized Losses on Available-for-Sale Securities, Gross		$ 4,900,000
Unrealized Loss as a Percent of Amortized Cost	1.00%	3.00%
Security Owned And Pledged As Collateral Amortized Cost	$ 709,000,000	$ 734,100,000
Security Owned and Pledged as Collateral, Fair Value	712,400,000	714,400,000
Marketable Securities, Unrealized Gain (Loss)	$ 928,000	$ (50,000)