CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Operating revenues:
Oil, gas, and NGL production revenue	$ 469,575	$ 362,595
Other operating revenues	14,605	14,828
Total operating revenues	484,180	377,423
Operating Expenses
Oil, gas, and NGL production expense	125,633	87,132
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	198,709	169,570
Exploration	15,398	18,607
Impairment of properties	21,521	142
General and administrative	32,280	28,142
Change in Net Profits Plan liability	(1,925)	3,939
Unrealized and Realized Derivative loss	30,572	2,216
Other operating expenses	15,794	11,450
Total operating expenses	437,982	321,198
Income from operations	46,198	56,225
Nonoperating Income (Expense)
Interest income	12	70
Interest expense	(19,101)	(14,278)
Income before income taxes	27,109	42,017
Income Tax Expense	(10,382)	(15,681)
Net income	$ 16,727	$ 26,336
Basic weighted-average common shares outstanding	66,211	64,104
Diluted weighted-average common shares outstanding	67,521	67,845
Basic net income per common share	$ 0.25	$ 0.41
Diluted net income per common share	$ 0.25	$ 0.39
Dividends per common share	$ 0.05	$ 0.05