Qualified Employee Benefit Plans - Amounts Recognized in Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Prior service cost	$ 24	$ 24	$ 24
Changes in employee benefit related items	(4,256)	(7,867)	1,610
Other comprehensive (loss) income	(4,443)
Retirement Plan
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Unrecognized net (loss) gain from experience different from that assumed and effects of changes and assumptions	(4,089)	(7,934)	1,870
Prior service cost	24	24	24
Changes in employee benefit related items	(4,065)	(7,910)	1,894
Income tax (expense) benefit	(216)	312	(207)
Other comprehensive (loss) income	$ (4,281)	$ (7,598)	$ 1,687

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- Definition

Amount, before tax, after reclassification adjustment, of increase (decrease) in accumulated other comprehensive income from gain (loss) of defined benefit plan.

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Amount of tax expense (benefit) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, before tax, of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

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Amount, before tax, after reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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