Condensed Consolidated Statements of Comprehensive Income - 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)	$ 29,459	$ (11,772)	$ 31,981	$ (22,775)
Other comprehensive income (loss):
Unrealized gain (loss) on derivatives (net of tax of ($2) and ($12) for the three months ended June 30, 2017 and 2016, respectively, and ($23) and $9 for the six months ended June 30, 2017 and 2016, respectively)	(3)	(20)	(39)	15
Unrealized loss on investments (net of tax of $0 and ($1) for the three months ended June 30, 2017 and 2016, respectively, and $0 and $(4) for the six months ended June 30 2017 and 2016, respectively)	0	(1)	0	(6)
Pension and other post-retirement benefits liability adjustment (net of tax of ($1,185) and $(1,227) for the three months ended June 30, 2017 and 2016, respectively, and ($845) and $(2,768) for the six months ended June 30, 2017 and 2016, respectively)	(1,967)	(2,036)	(1,402)	(4,594)
Comprehensive income (loss)	$ 27,489	$ (13,829)	$ 30,540	$ (27,360)