Supplemental Cash Flow Information - Supplemental Cash Flow Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net cash provided from operating activities included:
Income taxes paid (refunded from) to taxing authorities	$ 386	$ 675	$ (1,359)
Interest paid	153,249	133,103	116,766
Non-cash investing and financing activities included:
Asset retirement costs (removed) capitalized, net	57,982	24,061	(6,370)
Unproved property purchased with stock			$ 20,000