Accumulated Other Comprehensive Income, Reclassified (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Amortization of postretirement benefit plans [Abstract]
Prior service benefit		$ 0	$ (14)	$ 0	$ (27)
Unrecognized (gain) loss		(271)	115	(330)	390
Income tax expense		(81)	$ (164)	(57)	$ (272)
Total reclassifications for the period		(163)		(198)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Amortization of postretirement benefit plans [Abstract]
Prior service benefit	[1]	0		0
Unrecognized (gain) loss	[1]	(271)		(330)
Total before income tax		(271)		(330)
Income tax expense		108		132
Total reclassifications for the period		$ (163)		$ (198)

[1] These accumulated other comprehensive income components are included in the computation of net periodic postretirement benefit costs, which are included in selling, general and administrative expenses in our consolidated statements of operations (see Note 11 for additional details).