Supplemental Cash Flow Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net cash paid for:
Income taxes	$ 178	$ 43,505	$ 0
Interest, net of capitalized interest	8,942	273	0
Non-cash financing activities and investing activities:
Change in accrued capital expenditures	52,189	112,606	5,510
Conversion of debt securities to equity securities	9,400	0	0
Acquisition of exploration rights	8,000	0	0
Debt assumed from business acquisitions	40,691	3,184	0
Issuance of common stock for business acquisitions	284,100	72,700	0
Fixed assets additions under capital lease	$ 15,658	$ 0	$ 0