Pension and Postretirement Benefits Other Than Pension Plans - Pension Plans - Net Settlement Losses (Details) - Pension Plan [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment [Abstract]
Net settlement loss	$ 1,004	$ 1,218	$ 1,004	$ 1,218
Qualified Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment [Abstract]
Net settlement loss	$ 1,000	$ 1,200	$ 1,000	$ 1,200