Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net income (loss)	$ (149,226)	$ 102,121	$ (696,029)	$ 211,588
Net unrealized gain on derivative instruments qualifying as hedges:
Reclassification adjustment for loss on derivative instruments included in net income (loss), net of tax of $60 and $60 for the three months ended and $181 and $181 for the nine months ended in 2015 and 2014, respectively	100	100	299	299
Reclassification adjustment for (gain) loss on derivative instruments included in income (loss) from discontinued operations, net of tax of $0 and $(10) for the three months ended and $0 and $83 for the nine months ended in 2015 and 2014, respectively	0	(18)	0	140
Net unrealized gain on derivative instruments qualifying as hedges	100	82	299	439
Amortization of postretirement liability losses included in net periodic benefit cost (credit), net of tax of $233 and $159 for the three months ended and $881 and $477 for the nine months ended in 2015 and 2014, respectively	382	261	1,341	781
Foreign currency translation adjustment:
Foreign currency translation adjustment recognized during the period, net of tax of $(44) and $(89) for the three months ended and $(107) and $(36) for the nine months ended in 2015 and 2014, respectively	(73)	(146)	(176)	(58)
Reclassification adjustment for loss on foreign currency translation adjustment included in net income (loss), net of tax of $0 and $0 for the three months ended and $491 and $0 for the nine months ended in 2015 and 2014, respectively	0	0	802	0
Foreign currency translation adjustment	(73)	(146)	626	(58)
Net unrealized gain (loss) on available-for-sale investments:
Net unrealized loss on available-for-sale investments arising during the period, net of tax of $(19) and $(33) for the three months ended and $(57) and $(48) for the nine months ended in 2015 and 2014, respectively	(35)	(62)	(105)	(89)
Reclassification adjustment for loss on available-for-sale investments included in net income (loss), net of tax of $15 and $16 for the three months ended and $53 and $54 for the nine months ended in 2015 and 2014, respectively	28	31	98	100
Net unrealized gain (loss) on available-for-sale investments	(7)	(31)	(7)	11
Other comprehensive income	402	166	2,259	1,173
Comprehensive income (loss)	(148,824)	102,287	(693,770)	212,761
Comprehensive loss attributable to noncontrolling interest	(9,778)	(1,088)	(21,060)	(2,390)
Comprehensive income (loss) attributable to common stockholders	$ (139,046)	$ 103,375	$ (672,710)	$ 215,151