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
		Mar. 31, 2021	Mar. 31, 2020
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Level 3 assets, beginning of period	[1]	$ 2,047	$ 585
Net unrealized gains (losses) included in other comprehensive income	[1]		1
Realized gains (losses) and accretion (amortization) recognized in earnings	[1]	(84)	(25)
Settlements	[1]		(175)
Transfers into Level 3	[1]	2,214
Level 3 assets, end of period	[1]	$ 4,177	$ 386

[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.