Qualified Employee Benefit Plans - Reconciliation of Amounts Recognized in Other Comprehensive Income for the Retirement Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Recognized actuarial (loss) gain	$ (4,280)	$ (7,891)	$ 1,586
Amortization of prior service cost	24	24	24
Changes in employee benefit related items	4,256	7,867	(1,610)
Income tax (expense) benefit	(187)	274	(139)
Other comprehensive (loss) income	(4,443)
Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Recognized actuarial (loss) gain	(4,089)
Amortization of prior service cost	24	24	24
Changes in employee benefit related items	4,065	7,910	(1,894)
Income tax (expense) benefit	(216)
Other comprehensive (loss) income	(4,281)	$ (7,598)	$ 1,687
Retired Individual Plan
Defined Benefit Plan Disclosure [Line Items]
Recognized actuarial (loss) gain	(56)
Amortization of prior service cost	0
Changes in employee benefit related items	56
Income tax (expense) benefit	(2)
Other comprehensive (loss) income	(58)
Foreign Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Recognized actuarial (loss) gain	(135)
Amortization of prior service cost	0
Changes in employee benefit related items	135
Income tax (expense) benefit	31
Other comprehensive (loss) income	$ (104)