Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 29,481	$ 36,759	$ 62,884	$ (166,357)
Pension and postretirement plans:
Amortization of prior service cost, net of tax of ($42), ($42), ($86) and ($89), respectively	(71)	(71)	(141)	(149)
Amortization of net loss, including settlement charges, net of tax of $0, $0, $2 and $1,168, respectively	2	0	3	1,890
Current period change in fair value of pension and postretirement plans, net of tax of ($6) in 2016	0	0	0	(9)
Total pension and postretirement plans	(69)	(71)	(138)	1,732
Comprehensive Income (Loss)	$ 29,412	$ 36,688	$ 62,746	$ (164,625)