Qualified Employee Benefit Plans - Amounts Recognized in Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Prior service cost	$ 24	$ 24	$ 93
Changes in employee benefit related items	1,610	(3,166)	(2,950)
Other comprehensive income (loss)	1,471
Retirement Plan
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Unrecognized net gain (loss) from experience different from that assumed and effects of changes and assumptions	1,870	(3,043)	(3,115)
Prior service cost	24	24	93
Changes in employee benefit related items	1,894	(3,019)	(3,022)
Income tax expense	(207)	(49)	(10)
Other comprehensive income (loss)	$ 1,687	$ (3,068)	$ (3,032)

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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, after tax, before reclassification adjustment, of (increase) decrease in accumulated other comprehensive income of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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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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