Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - Supplemental Retirement Plan [Member] - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Net periodic benefit cost [Abstract]
Service cost	$ 27	$ 29
Interest cost	541	495
Amortization of prior service cost	63	63
Recognized net actuarial loss	162	226
Net periodic benefit cost	$ 793	$ 813

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

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Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.

+ References

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- Definition

Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of net periodic benefit cost (credit) for defined benefit plan.

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- Definition

Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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