Investments - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Proceeds from sale of available-for-sale debt securities	$ 31,700,000	$ 101,200,000	$ 33,700,000
Gross realized gains	27,000	4,600,000	274,000
Gross realized losses	6,000	0	53,000
Amount payable for securities purchased	1,000,000.0	1,700,000	2,100,000
Amount receivable for securities sold	523,000	809,000	$ 6,000
Other than temporary impairments losses, investments	0
Investments	1,200,000
Deposits held in trust accounts	8,500,000	8,800,000
Deposits, held in trust for collateral requirements	$ 76,100,000	$ 67,600,000