Consolidated statements of cash flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash flows from operating activities:
Net income	$ 37,221	$ 57,210
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income tax expense	21,601	32,181
Depreciation, depletion and amortization	131,364	112,220
Non-cash stock-based compensation	7,680	4,835
Accretion of asset retirement obligations	804	556
Unrealized (gain) loss on derivative financial instruments, net	(2,449)	(16,929)
Premiums paid for derivative financial instruments	(5,249)	(2,927)
Amortization of premiums paid for derivative financial instruments	282	319
Amortization of deferred loan costs	2,627	2,268
Other	74	(81)
(Increase) decrease in accounts receivable	(6,591)	2,303
(Increase) decrease in other current assets	(894)	(3,075)
Increase (decrease) in accounts payable	(16,568)	3,304
Increase (decrease) in undistributed revenues and royalties	4,327	4,721
Increase (decrease) in accrued compensation and benefits	(293)	(3,060)
Increase (decrease) in other accrued liabilities	1,777	4,828
Increase (decrease) in other noncurrent liabilities	422	89
Increase (decrease) in fair value of performance unit awards	2,155	1,028
Net cash provided by operating activities	178,290	199,790
Capital expenditures:
Investment in equity method investee	(3,287)	0
Oil and natural gas properties	(375,901)	(473,846)
Pipeline and gas gathering assets	(8,302)	(7,031)
Other fixed assets	(8,803)	(4,988)
Proceeds from other fixed asset disposals	0	34
Net cash used in investing activities	(396,293)	(485,831)
Cash flows from financing activities:
Borrowings on revolving credit facilities	230,000	195,000
Payments on revolving credit facility	0	280,000
Issuance of 2022 Notes	0	500,000
Purchase of treasury stock	(919)	0
Payments for loan costs	714	10,476
Net cash provided by financing activities	228,367	404,524
Net decrease in cash and cash equivalents	10,364	118,483
Cash and cash equivalents, beginning of period	33,224	28,002
Cash and cash equivalents, end of period	43,588	146,485
Supplemental disclosure of cash flow information:
Cash paid for interest, net of $212 and $505, respectively, of capitalized interest	48,348	27,956
Change in accrued capital expenditures	(33,892)	1,624
Capitalized asset retirement cost	$ 1,262	$ 2,270