Fair Value of Financial Instruments - Rollforward of Level 3 Assets Measured on Recurring Basis (Details) - Fair Value, Recurring Measurements [Member] - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Level 3 assets, beginning of period		$ 3,336	$ 5,268	$ 2,047	[1]	$ 585	[1]
Net unrealized gains (losses) included in other comprehensive income		1		1	[1]	2	[1]
Realized gains (losses) and accretion (amortization) recognized in earnings		(125)	(444)	(359)	[1]	(452)	[1]
Purchases		2,068	2,999	3,067	[1]	2,999	[1]
Settlements		(1)	(4,624)	(2,191)	[1]	(4,970)	[1]
Transfers into Level 3	[1]			2,714		5,035
Transfers out of Level 3		(1,501)		(1,501)	[1]
Level 3 assets, end of period	[1]	$ 3,778	$ 3,199	$ 3,778		$ 3,199

[1] Activities for investments that enter Level 3 in one quarter and exit Level 3 in another quarter within the same fiscal year are not eliminated until year-end when only the full year amounts are presented.