Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income	$ 58,810	$ 26,611	$ (8,468)
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	113,581	104,624	104,561
Accretion of liability for asset retirement obligations	15,565	15,942	12,845
Unrealized loss (gain) on derivative contracts	9,491	(11,475)	(3,500)
Non-cash compensation	4,717	2,509	1,255
In-kind interest on PIK Notes			(3,395)
Deferred income taxes	29,900	14,822	(4,409)
Exploration expenditures	4,227	11,239	5,103
Impairments	8,883	32,466	26,142
Amortization of deferred financing costs and discount on debt	2,556	1,657	1,130
Loss on early extinguisment of debt		2,377
Other	2,448	6,984	(90)
Changes in operating assets and liabilities:
Trade accounts receivable	(33,547)	(10,037)	6,515
Other receivables		2,088	3,376
Prepaid expenses	1,047	(7,623)	(363)
Other assets	145	(1,215)	618
Accounts payable and accrued expenses	31,477	12,650	2,361
Asset retirement obligations	(35,429)	(32,364)	(16,130)
Other liabilities		(3)	(171)
Net cash provided by operating activities	213,871	171,252	127,380
Cash flows used in investing activities:
Decrease in restricted cash		2,466	13,658
Property acquisitions	(578,372)	(235,486)	(623)
Exploration and development expenditures	(184,850)	(76,003)	(58,183)
Other property and equipment additions	(1,743)	(1,568)	(755)
Net cash used in investing activities	(764,965)	(310,591)	(45,903)
Cash flows provided by (used in) financing activities:
Proceeds from indebtedness	509,313	203,794	20,394
Repayments of indebtedness	(20,000)		(94,882)
Deferred financing costs	(8,469)	(6,646)	(181)
Purchase of shares into treasury	(8,798)	(11,353)
Exercise of stock options	441	119
Net cash provided by (used in) financing activities	472,487	185,914	(74,669)
Net increase (decrease) in cash and cash equivalents	(78,607)	46,575	6,808
Cash and cash equivalents at beginning of period	80,128	33,553	26,745
Cash and cash equivalents at end of period	1,521	80,128	33,553
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Debt incurred to pay deferred financing costs and surety bond premium			737
Interest	$ 21,129	$ 9,395	$ 8,307