Retirement Plans, Summary of Funded Status at End of Year (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan [Member]
Funded status at end of year [Abstract]
Fair value of plan assets	$ 303,151	$ 294,995	$ 257,517
Benefit obligations	(381,483)	(354,994)	(337,176)
Funded status and amount recognized at end of year	(78,332)	(59,999)
SERP [Member]
Funded status at end of year [Abstract]
Fair value of plan assets	0	0	0
Benefit obligations	(1,246)	(1,412)	(1,457)
Funded status and amount recognized at end of year	(1,246)	(1,412)
Other Postretirement Benefits [Member]
Funded status at end of year [Abstract]
Fair value of plan assets	0	0	0
Benefit obligations	(743)	(679)	$ (675)
Funded status and amount recognized at end of year	$ (743)	$ (679)

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

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- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References

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- Definition

Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

+ References

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- References

No definition available.

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- Details

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