Pension and Other Postretirement Benefits Costs - Schedule of Amount Recognized in AOCL (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
AOCL, Prior Service Costs (Credit)	$ 0	$ 0
AOCL, Net Actuarial Loss	11,537	13,266
AOCL, Total	11,537	13,266
Pension Costs [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory Assets, Prior Service Cost (Credit)	7	49
Regulatory Assets, Net Actuarial Loss	170,535	175,035
Regulatory Assets, Total	170,542	175,084
Postretirement Benefit Costs [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory Assets, Prior Service Cost (Credit)	(1,738)	(2,206)
Regulatory Assets, Net Actuarial Loss	6,189	6,964
Regulatory Assets, Total	$ 4,451	$ 4,758