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Benefit Plans - Changes to Benefit Obligations and Fair Value of Plan Assets and Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Funded status and amounts recognized in balance sheets
Pension liabilities for underfunded plans				$ (138,222)	$ (127,909)
Pension Benefits
Changes to PBO or APBO
Benefit obligation at beginning of year	$ 199,072	$ 212,981
Service cost	14	696
Interest cost	8,261	7,362
Actuarial loss (gain)	22,573	(6,619)
Curtailment gain	(1,061)
Benefit payments	(15,574)	(15,348)
Benefit obligation at end of year	213,285	199,072	$ 212,981
Changes to fair value of plan assets
Fair value of plan assets at beginning of year	99,581	114,220
Actual return on plan assets	20,863	(6,936)
Benefit payments from trust	(7,785)	(7,703)
Fair value of plan assets at end of year	112,659	99,581	114,220
Funded status and amounts recognized in balance sheets
Pension assets for overfunded plans				16,291	8,702
Pension liabilities for underfunded plans				(116,917)	(108,193)
Funded status				(100,626)	(99,491)
PBO, ABO and fair value of plan assets
Projected benefit obligation	213,285	199,072	212,981	213,285	199,072
Accumulated benefit obligation				213,202	197,236
Fair value of plan assets	99,581	99,581	114,220	112,659	99,581
Overfunded (underfunded) portion of PBO/ABO				(100,626)	(99,491)
Pension Benefits \| Funded Plan
Changes to PBO or APBO
Benefit obligation at beginning of year	90,879
Interest cost	3,808	3,420	3,922
Benefit obligation at end of year	96,368	90,879
Changes to fair value of plan assets
Fair value of plan assets at beginning of year	99,581
Fair value of plan assets at end of year	112,659	99,581
PBO, ABO and fair value of plan assets
Projected benefit obligation	90,879	90,879		96,368	90,879
Accumulated benefit obligation				96,368	90,879
Fair value of plan assets	99,581	99,581		112,659	99,581
Overfunded (underfunded) portion of PBO/ABO				16,291	8,702
Pension Benefits \| Unfunded Plan
Changes to PBO or APBO
Benefit obligation at beginning of year	108,193
Benefit obligation at end of year	116,917	108,193
PBO, ABO and fair value of plan assets
Projected benefit obligation	108,193	108,193		116,917	108,193
Accumulated benefit obligation				116,834	106,357
Overfunded (underfunded) portion of PBO/ABO				(116,917)	(108,193)
Other Benefits
Changes to PBO or APBO
Benefit obligation at beginning of year	19,716	21,449
Service cost	710	750
Interest cost	808	739
Actuarial loss (gain)	540	(2,755)
Benefit payments	(469)	(467)
Benefit obligation at end of year	21,305	19,716	21,449
Funded status and amounts recognized in balance sheets
Pension liabilities for underfunded plans				(21,305)	(19,716)
Funded status				(21,305)	(19,716)
PBO, ABO and fair value of plan assets
Projected benefit obligation	$ 21,305	$ 21,449	$ 21,449	$ 21,305	$ 19,716