Consolidated Statements of Income and Comprehensive Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Revenues:
Gas sales	$ 126,547	$ 69,741	$ 227,668	$ 154,894
Oil sales	304,466	229,210	561,998	496,294
NGL sales	52,309	44,286	109,184	103,300
Gas gathering, processing and other	10,844	10,179	21,571	21,886
Gas marketing, net	(409)	(294)	(308)	(216)
Total revenues	493,757	353,122	920,113	776,158
Costs and expenses:
Depreciation, depletion and amortization	147,231	121,237	283,669	239,499
Asset retirement obligation	2,884	2,441	5,283	5,966
Production	69,433	62,494	138,819	130,119
Transportation and other operating	22,022	13,169	40,656	26,485
Gas gathering and processing	5,184	4,955	11,340	9,806
Taxes other than income	27,807	23,483	52,935	48,643
General and administrative	22,836	12,634	38,413	26,781
Stock compensation	3,507	4,684	7,112	9,218
Gain on derivative instruments, net	(13,660)	(10,078)	(12,057)	(5,990)
Other operating, net	2,365	2,719	5,297	5,059
Total costs and expenses	289,609	237,738	571,467	495,586
Operating income	204,148	115,384	348,646	280,572
Other (income) and expense:
Interest expense	14,112	13,679	27,318	22,347
Capitalized interest	(7,387)	(9,119)	(16,582)	(16,923)
Loss on early extinguishment of debt		16,214		16,214
Other, net	(8,758)	(7,829)	(11,374)	(12,555)
Income before income tax	206,181	102,439	349,284	271,489
Income tax expense	76,616	38,137	129,792	101,080
Net income	129,565	64,302	219,492	170,409
Basic
Distributed (in dollars per share)	$ 0.14	$ 0.12	$ 0.28	$ 0.24
Undistributed (in dollars per share)	$ 1.36	$ 0.63	$ 2.26	$ 1.74
Total basic (in dollars per share)	$ 1.50	$ 0.75	$ 2.54	$ 1.98
Diluted
Distributed (in dollars per share)	$ 0.14	$ 0.12	$ 0.28	$ 0.24
Undistributed (in dollars per share)	$ 1.35	$ 0.62	$ 2.25	$ 1.73
Total diluted (in dollars per share)	$ 1.49	$ 0.74	$ 2.53	$ 1.97
Comprehensive income:
Net income	129,565	64,302	219,492	170,409
Other comprehensive income:
Change in fair value of investments, net of tax	19	(135)	99	264
Total comprehensive income	$ 129,584	$ 64,167	$ 219,591	$ 170,673