Pension and Other Postretirement Benefits Costs - Schedule of Amounts Realized in Other Comprehensive Loss (Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory Asset, Net actuarial loss (gain)	$ (14,261)	$ (12,177)	$ (14,005)
Settlement Loss	0	0	0
Regulatory Asset, Prior service cost	(42)	(127)	(230)
Regulatory Asset, Actuarial loss	(18,761)	(14,802)	(13,238)
Regulatory Asset, Total	(4,542)	(2,752)	537
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory Asset, Net actuarial loss (gain)	327	214	1,488
Settlement Loss	0	0	0
Regulatory Asset, Prior service cost	468	468	468
Regulatory Asset, Actuarial loss	(448)	(696)	(705)
Regulatory Asset, Total	(307)	(442)	(1,725)
Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Amounts reclassified to AOCL	(677)	2,777	(1,196)
Settlement Loss	0	0	193
Other Comprehensive Loss (Income), Prior service cost	0	0	0
Loss from plan settlement	(1,052)	(946)	1,386
Total reclassifications before tax	$ (1,729)	$ 1,831	$ 383