Supplemental Disclosures to the Consolidated Statements of Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net cash provided by operating activities included:
Cash payments for interest	$ 107,122	$ 103,350	$ 85,222
Interest capitalized	(15,995)	(4,437)	(2,379)
Cash payments for interest, net of amounts capitalized	91,127	98,913	82,843
Cash payments for income taxes	641	255	179
Non-cash investing activities included:
Asset retirement obligation additions and revisions	9,036	1,079	2,522
Oil and natural gas properties acquired through increase (decrease) in accounts payable and accrued liabilities	27,875	24,280	(14,667)
Modification of Time Vesting equity awards to liability plan	$ 0	$ 0	$ 2,640