Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Segment Information
Number of reportable segments			3
Revenues:
Total Revenues	$ 773,000	$ 410,622	$ 1,181,734	$ 722,671
Segment operating income (loss):
Operating income	153,649	170,233	273,416	241,540
Less interest expense, net	(31,887)	(3,887)	(35,287)	(8,483)
Other income			24,503	24,503
Income from continuing operations before income tax expense	146,265	166,346	262,632	233,057
Income tax expense	38,907	50,236	73,461	74,252
Income from continuing operations	107,358	116,110	189,171	158,805
Depreciation and depletion:
Total depreciation and depletion	89,426	23,885	117,784	46,054
Capital Expenditures:
Total capital expenditures	92,124	30,703	136,417	45,040
Identifiable Assets:
Total identifiable assets	7,150,350		7,150,350		1,657,765
U.S. Operations
Revenues:
Total Revenues	506,852	410,034	914,788	721,305
Segment operating income (loss):
Operating income	168,671	182,067	307,644	261,492
Depreciation and depletion:
Total depreciation and depletion	39,269	23,798	67,438	45,890
Capital Expenditures:
Total capital expenditures	40,972	26,784	85,108	40,861
Identifiable Assets:
Total identifiable assets	963,205		963,205		1,021,534
Canadian and U.K. operations
Revenues:
Total Revenues	265,575		265,575
Segment operating income (loss):
Operating income	12,448		12,448
Depreciation and depletion:
Total depreciation and depletion	49,965		49,965
Capital Expenditures:
Total capital expenditures	51,411		51,411
Identifiable Assets:
Total identifiable assets	5,709,816		5,709,816
Other
Revenues:
Total Revenues	573	588	1,371	1,366
Segment operating income (loss):
Operating income	(27,470)	(11,834)	(46,676)	(19,952)
Depreciation and depletion:
Total depreciation and depletion	192	87	381	164
Capital Expenditures:
Total capital expenditures	(259)	3,919	(102)	4,179
Identifiable Assets:
Total identifiable assets	$ 477,329		$ 477,329		$ 636,231