Condensed Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
REVENUES
Oil and natural gas sales	$ 266,772	$ 233,653
Electricity sales	7,589	5,980
Natural gas marketing	2,027	1,859
Gain on sale of assets	23	1,763
Interest and other income, net	475	747
TOTAL REVENUES	276,886	244,002
EXPENSES
Operating costs—oil and natural gas production	86,148	54,221
Operating costs- electricity generation	5,296	5,017
Production taxes	10,784	10,658
Depreciation, depletion & amortization	68,478	48,422
Natural gas marketing	1,878	1,777
General and administrative	22,278	17,741
Interest	24,687	20,104
Dry hole, abandonment, impairment and exploration	962	3,067
Impairment of oil and natural gas properties	2,467	0
Realized and unrealized loss on derivatives, net	737	28,481
TOTAL EXPENSES	223,715	189,488
Earnings before income taxes	53,171	54,514
Income tax provision	20,737	20,616
Net earnings	32,434	33,898
Basic net earnings per share (in dollars per share)	$ 0.59	$ 0.62
Diluted net earnings per share (in dollars per share)	$ 0.58	$ 0.61
Dividends per share (in dollars per share)	$ 0.08	$ 0.08
Oil and Natural Gas Properties, Buildings, and Equipment
EXPENSES
Depreciation, depletion & amortization	68,084	47,956
Electricity Generation
EXPENSES
Depreciation, depletion & amortization	$ 394	$ 466