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		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Level 3 assets, beginning of period		$ 386	$ 381	$ 585	[1]	$ 921	[1]
Net unrealized gains (losses) included in other comprehensive income		1	(7)	2	[1]	(13)	[1]
Realized gains (losses) and accretion (amortization) recognized in earnings		17	(32)	(8)	[1]	(24)	[1]
Settlements		(171)	(152)	(346)	[1]	(196)	[1]
Transfers into Level 3		5,035	836	5,035	[1]	836	[1]
Transfers out of Level 3	[1]					(498)
Level 3 assets, end of period	[1]	$ 5,268	$ 1,026	$ 5,268		$ 1,026

[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.