Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Consolidated Statements of Comprehensive Income [Abstract]
Net income (loss)	$ (309,445)	$ 56,139
Other comprehensive income:
Reclassification adjustment for loss on derivative instruments included in net income, net of tax of $60 and $204 for the three months ended in 2015 and 2014, respectively	99	344
Amortization of postretirement liability losses included in net periodic benefit cost, net of tax of $230 and $168 for the three months ended in 2015 and 2014, respectively	375	275
Foreign currency translation adjustment:
Foreign currency translation adjustment recognized during the period, net of tax of $(68) and $28 for the three months ended in 2015 and 2014, respectively	(112)	46
Reclassification adjustment for loss on foreign currency translation adjustment included in net income, net of tax of $490 and $0 for the three months ended in 2015 and 2014, respectively	802	0
Foreign currency translation adjustment	690	46
Net unrealized gain on available-for-sale investments:
Net unrealized loss on available-for-sale investments arising during the period, net of tax of $(11) and $(19) for the three months ended in 2015 and 2014, respectively	(21)	(36)
Reclassification adjustment for loss on available-for-sale investments included in net income, net of tax of $19 and $20 for the three months ended in 2015 and 2014, respectively	36	38
Net unrealized gain on available-for-sale investments	15	2
Other comprehensive income	1,179	667
Comprehensive income (loss)	(308,266)	56,806
Comprehensive loss attributable to noncontrolling interest	(3,528)	(523)
Comprehensive income (loss) attributable to common stockholders	$ (304,738)	$ 57,329