Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net income (loss)	$ (237,358)	$ 53,327	$ (546,803)	$ 109,466
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 $121 and $121 for the six months ended in 2015 and 2014, respectively	100	100	199	199
Reclassification adjustment for (gain) loss on derivative instruments included in income (loss) from discontinued operations, net of tax of $0 and $(50) for the three months ended and $0 and $93 for the six months ended in 2015 and 2014, respectively	0	(87)	0	158
Net unrealized gain on derivative instruments qualifying as hedges	100	13	199	357
Amortization of postretirement liability losses included in net periodic benefit cost, net of tax of $420 and $150 for the three months ended and $649 and $318 for the six months ended in 2015 and 2014, respectively	584	245	959	520
Foreign currency translation adjustment:
Foreign currency translation adjustment recognized during the period, net of tax of $6 and $26 for the three months ended and $(63) and $54 for the six months ended in 2015 and 2014, respectively	9	42	(103)	88
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 six months ended in 2015 and 2014, respectively	0	0	802	0
Foreign currency translation adjustment	9	42	699	88
Net unrealized gain (loss) on available-for-sale investments:
Net unrealized gain (loss) on available-for-sale investments arising during the period, net of tax of $(23) and $4 for the three months ended and $(34) and $5 for the six months ended in 2015 and 2014, respectively	(43)	8	(64)	10
Reclassification adjustment for loss on available-for-sale investments included in net income (loss), net of tax of $15 and $17 for the three months ended and $34 and $17 for the six months ended in 2015 and 2014, respectively	28	32	64	32
Net unrealized gain (loss) on available-for-sale investments	(15)	40	0	42
Other comprehensive income	678	340	1,857	1,007
Comprehensive income (loss)	(236,680)	53,667	(544,946)	110,473
Comprehensive loss attributable to noncontrolling interest	(7,754)	(779)	(11,282)	(1,302)
Comprehensive income (loss) attributable to common stockholders	$ (228,926)	$ 54,446	$ (533,664)	$ 111,775