Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities:
Net income	$ 85,274	$ 58,810	$ 26,611
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	200,359	113,581	104,624
Accretion of liability for asset retirement obligations	28,299	15,565	15,942
Change in fair value of derivative instruments	20,884	9,491	(11,475)
Non-cash compensation	7,344	4,717	2,509
Deferred income taxes	49,687	29,900	14,822
Exploration expenditures	5,520	4,227	11,239
Impairments	2,937	8,883	32,466
Amortization of deferred financing costs and discount on debt	5,396	2,556	1,657
Gain on sale of assets	(28,681)
Loss on early extinguisment of debt			2,377
Other	27,235	2,448	6,984
Changes in operating assets and liabilities:
Trade accounts receivable	(1,916)	(33,547)	(10,037)
Other receivables			2,088
Prepaid expenses	2,081	1,047	(7,623)
Other assets	790	145	(1,215)
Accounts payable and accrued expenses	35,658	31,477	12,650
Asset retirement obligation settlements	(53,308)	(35,429)	(32,364)
Other liabilities			(3)
Net cash provided by operating activities	387,559	213,871	171,252
Cash flows used in investing activities:
Decrease in restricted cash			2,466
Property acquisitions	(27,560)	(578,372)	(235,486)
Deposit for Nexen Acquisition	(7,040)
Exploration and development expenditures	(322,040)	(184,850)	(76,003)
Other property and equipment additions	(2,016)	(1,743)	(1,568)
Proceeds from sale of assets	52,317
Net cash used in investing activities	(306,339)	(764,965)	(310,591)
Cash flows provided by (used in) financing activities:
Proceeds from indebtedness		509,313	203,794
Repayments of indebtedness	(65,000)	(20,000)
Deferred financing costs	(674)	(8,469)	(6,646)
Purchase of shares into treasury	(9,640)	(8,798)	(11,353)
Exercise of stock options	1,385	441	119
Net cash provided by (used in) financing activities	(73,929)	472,487	185,914
Net increase (decrease) in cash and cash equivalents	7,291	(78,607)	46,575
Cash and cash equivalents at beginning of period	1,521	80,128	33,553
Cash and cash equivalents at end of period	8,812	1,521	80,128
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest	$ 47,339	$ 21,129	$ 9,395