Supplemental Cash Flow Information - Summary of Supplemental Cash Flow Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplemental cash flow information:
Cash paid for interest	$ 102,043	$ 70,088	$ 36,845
Cash paid for income taxes	829	16,030	10,879
Cash received for income tax refunds	(13,866)	(116)	(1,406)
Non-cash investing activities:
Increase in accrued capital expenditures	49,039	173,591	147,997
Acquisition of assets through issuance of common stock	176,563
Asset retirement obligations, net	$ 3,808	$ 5,506	$ 5,358