Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities:
Net income	$ 34,657	$ 33,952
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	78,932	73,081
Accretion of liability for asset retirement obligations	10,031	12,172
Unrealized loss (gain) on derivative contracts	8,052	(31,122)
Non-cash compensation	3,493	1,833
Deferred income taxes	16,134	20,117
Exploration expenditures	4,097	147
Impairments	6,206	19,197
Amortization of deferred financing costs and discount on debt	1,516	1,152
Loss on early extinguishment of debt		2,377
Other	3,405	4,611
Changes in operating assets and liabilities:
Trade accounts receivable	5,171	(6,430)
Other receivables		1,283
Prepaid expenses	4,062	(5,207)
Other assets	362	(862)
Accounts payable and accrued expenses	14,149	5,563
Asset retirement obligations	(27,647)	(25,926)
Other liabilities		(3)
Net cash provided by operating activities	162,620	105,935
Cash flows used in investing activities:
Decrease in restricted cash		2,467
Property acquisitions	(34,458)	(196,533)
Deposit for Hilcorp Acquisition	(55,000)
Exploration and development expenditures	(135,950)	(49,246)
Other property and equipment additions	(1,474)	(833)
Net cash used in investing activities	(226,882)	(244,145)
Cash flows provided by (used in) financing activities:
Proceeds from indebtedness		203,794
Deferred financing costs	(6)	(6,465)
Purchase of shares into treasury	(8,798)	(5,523)
Exercise of stock options	257	119
Net cash provided by (used in) financing activities	(8,547)	191,925
Net increase (decrease) in cash and cash equivalents	(72,809)	53,715
Cash and cash equivalents at beginning of period	80,128	33,553
Cash and cash equivalents at end of period	$ 7,319	$ 87,268