Accumulated Other Comprehensive Income, Reclassified (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Amortization of postretirement benefit plans [Abstract]
Prior service benefit	$ 0	[1]	$ 0	[1]	$ (54)
Unrecognized (gain) loss	(268)	[1]	(661)	[1]	$ 763
Total before income tax	(268)		(661)
Income tax expense	107		264
Total reclassifications for the period	$ (161)		$ (397)

[1] These accumulated other comprehensive income components are included in the computation of net periodic postretirement benefit costs, which are included in other non-operating income (expense), net in our consolidated statements of operations (see Note 17 for additional information).