Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Revenues:
Total Revenues	$ 441,496	$ 677,574	$ 932,839	$ 1,309,137
Segment operating income (loss):
Total operating income (loss)	(30,553)	67,973	(94,173)	152,049
Less interest expense, net	(52,985)	(30,763)	(104,953)	(58,553)
Other loss, net	(714)	(5,919)	(609)	(12,912)
Income (loss) from continuing operations before income tax expense (benefit)	(84,252)	31,291	(199,735)	80,584
Income tax expense (benefit)	(49,760)	4,535	(115,799)	13,212
Income (loss) from continuing operations	(34,492)	26,756	(83,936)	67,372
Depreciation and depletion:
Total depreciation and depletion	68,320	74,459	149,510	140,952
Capital expenditures:
Total capital expenditures	46,224	125,211	80,251	246,056
Identifiable assets by segment:
Total identifiable assets	5,731,856		5,731,856		5,768,420
U.S. Operations
Revenues:
Total Revenues	321,009	466,761	660,234	918,911
Segment operating income (loss):
Total operating income (loss)	37,333	107,245	30,376	214,226
Depreciation and depletion:
Total depreciation and depletion	31,189	43,704	78,662	85,846
Capital expenditures:
Total capital expenditures	38,803	43,851	66,204	79,963
Identifiable assets by segment:
Total identifiable assets	1,199,787		1,199,787		1,603,745
Canadian and U.K. operations
Revenues:
Total Revenues	119,873	209,645	271,317	387,996
Segment operating income (loss):
Total operating income (loss)	(66,347)	(24,679)	(115,113)	(38,234)
Depreciation and depletion:
Total depreciation and depletion	36,620	30,535	69,852	54,671
Capital expenditures:
Total capital expenditures	7,231	78,177	13,545	162,357
Identifiable assets by segment:
Total identifiable assets	3,800,009		3,800,009		3,728,817
Other
Revenues:
Total Revenues	614	1,168	1,288	2,230
Segment operating income (loss):
Total operating income (loss)	(1,539)	(14,593)	(9,436)	(23,943)
Depreciation and depletion:
Total depreciation and depletion	511	220	996	435
Capital expenditures:
Total capital expenditures	190	3,183	502	3,736
Identifiable assets by segment:
Total identifiable assets	$ 732,060		$ 732,060		$ 435,858