Supplemental Disclosures to the Consolidated Statements of Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Net cash provided by operating activities included:
Cash payments for interest	$ 74,446	$ 70,735
Interest capitalized	(9,957)	(11,670)
Cash payments for interest, net of amounts capitalized	64,489	59,065
Cash payments for income taxes	591	240
Non-cash investing activities included:
Asset retirement obligation additions and revisions	7,118	1,036
Oil and Natural Gas Properties Acquired Through Increase (Decrease) in Accounts Payable and Accrued Liabilities	$ 22,458	$ 8,298