Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net income (loss)	$ 97,332	$ 34,657
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	153,847	78,932
Accretion of liability for asset retirement obligations	18,464	10,031
Unrealized loss (gain) on derivative contracts	(822)	8,052
Non-cash compensation	5,358	3,493
Deferred income taxes	55,239	16,134
Exploration expenditures	3,764	4,097
Impairments	2,183	6,206
Amortization of deferred financing costs and discount on debt	4,016	1,516
Gain on sale of assets	(28,601)
Other	27,982	3,405
Changes in operating assets and liabilities:
Trade accounts receivable	(1,718)	5,171
Prepaid expenses	(5,308)	4,062
Other assets	(1,077)	362
Accounts payable and accrued expenses	15,345	14,149
Asset retirement obligation settlements	(36,843)	(27,647)
Net cash provided by (used in) operating activities	309,161	162,620
Cash flows provided by (used) in investing activities:
Property acquisitions	(26,979)	(34,458)
Deposit for Hilcorp Acqusition		(55,000)
Exploration and development expenditures	(252,125)	(135,950)
Other property and equipment additions	(1,517)	(1,474)
Proceeds from sale of assets	52,237
Net cash provided by (used in) investing activities	(228,384)	(226,882)
Cash flows provided by (used in) financing activities:
Repayments of indebtedness	(70,000)
Deferred financing costs	(670)	(6)
Purchase of shares into treasury	(9,640)	(8,798)
Exercise of stock options	951	257
Net cash provided by (used in) financing activities	(79,359)	(8,547)
Net increase (decrease) in cash and cash equivalents	1,418	(72,809)
Cash and cash equivalents at beginning of period	1,521	80,128
Cash and cash equivalents at end of period	$ 2,939	$ 7,319