Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Revenues:
Total Revenues	$ 491,343	$ 631,563
Segment operating income (loss):
Total operating income (loss)	(63,620)	84,076
Less interest expense, net	(51,968)	(27,790)
Other income (loss)	105	(6,993)
Income (loss) before income tax expense	(115,483)	49,293
Income tax expense (benefit)	(66,039)	8,677
Net income (loss)	(49,444)	40,616
Depreciation and depletion:
Total depreciation and depletion	81,190	66,493
Capital expenditures:
Total capital expenditures	34,027	120,845
Identifiable assets by segment:
Total identifiable assets	5,883,442		5,768,420
U.S. Operations
Revenues:
Total Revenues	339,225	452,150
Segment operating income (loss):
Total operating income (loss)	(6,957)	106,981
Depreciation and depletion:
Total depreciation and depletion	47,473	42,142
Capital expenditures:
Total capital expenditures	27,401	36,112
Identifiable assets by segment:
Total identifiable assets	1,438,289		1,603,745
Canadian and U.K. operations
Revenues:
Total Revenues	151,444	178,351
Segment operating income (loss):
Total operating income (loss)	(48,766)	(13,555)
Depreciation and depletion:
Total depreciation and depletion	33,232	24,136
Capital expenditures:
Total capital expenditures	6,314	84,180
Identifiable assets by segment:
Total identifiable assets	3,918,439		3,728,817
Other
Revenues:
Total Revenues	674	1,062
Segment operating income (loss):
Total operating income (loss)	(7,897)	(9,350)
Depreciation and depletion:
Total depreciation and depletion	485	215
Capital expenditures:
Total capital expenditures	312	553
Identifiable assets by segment:
Total identifiable assets	$ 526,714		$ 435,858