Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 segment	Sep. 30, 2010	Dec. 31, 2010
Segment Information
Number of reportable segments			3
Revenues:
Total Revenues	$ 690,069	$ 464,262	$ 1,871,803	$ 1,186,933
Segment operating income (loss):
Operating income	148,650	207,787	422,066	449,327
Less interest expense, net	(27,602)	(4,004)	(62,889)	(12,487)
Other income (loss), net	(13,143)		11,360
Income from continuing operations before income tax expense	107,905	203,783	370,537	436,840
Income tax expense	31,684	66,811	105,145	141,063
Income from continuing operations	76,221	136,972	265,392	295,777
Depreciation and depletion:
Total depreciation and depletion	63,046	25,905	180,830	71,959
Capital Expenditures:
Total capital expenditures	156,960	35,190	293,377	80,230
Identifiable Assets:
Total identifiable assets	7,171,947		7,171,947		1,657,765
U.S. Operations
Revenues:
Total Revenues	467,130	463,478	1,381,918	1,184,783
Segment operating income (loss):
Operating income	112,867	215,518	420,511	477,010
Depreciation and depletion:
Total depreciation and depletion	46,732	25,733	114,170	71,623
Capital Expenditures:
Total capital expenditures	41,435	35,147	126,543	76,008
Identifiable Assets:
Total identifiable assets	1,141,890		1,141,890		1,021,534
Canadian and U.K. operations
Revenues:
Total Revenues	222,681		488,256
Segment operating income (loss):
Operating income	50,195		62,643
Depreciation and depletion:
Total depreciation and depletion	16,124		66,089
Capital Expenditures:
Total capital expenditures	115,426		166,837
Identifiable Assets:
Total identifiable assets	5,537,155		5,537,155
Other
Revenues:
Total Revenues	258	784	1,629	2,150
Segment operating income (loss):
Operating income	(14,412)	(7,731)	(61,088)	(27,683)
Depreciation and depletion:
Total depreciation and depletion	190	172	571	336
Capital Expenditures:
Total capital expenditures	99	43	(3)	4,222
Identifiable Assets:
Total identifiable assets	$ 492,902		$ 492,902		$ 636,231