Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 128,555	$ 4,531
Receivables, net	449,456	367,754
Oil and gas well equipment and supplies	85,278	66,772
Deferred income taxes	13,725	16,854
Derivative instruments		4,268
Prepaid expenses	7,906	7,867
Other current assets	1,432	1,093
Total current assets	686,352	469,139
Oil and gas properties at cost, using the full cost method of accounting:
Proved properties	13,801,249	12,863,961
Unproved properties and properties under development, not being amortized	886,361	585,361
Gross oil and gas properties	14,687,610	13,449,322
Less - accumulated depreciation, depletion and amortization	(7,838,007)	(7,483,685)
Net oil and gas properties	6,849,603	5,965,637
Fixed assets, net	182,521	146,918
Goodwill	620,232	620,232
Other assets, net	60,299	51,209
Total assets	8,399,007	7,253,135
Current liabilities:
Accounts payable	126,259	116,110
Accrued liabilities	468,952	412,495
Derivative instruments	8,506	389
Revenue payable	197,473	154,173
Total current liabilities	801,190	683,167
Long-term debt	1,500,000	924,000
Deferred income taxes	1,626,206	1,459,841
Other liabilities	184,980	163,919
Total liabilities	4,112,376	3,230,927
Stockholders' equity:
Preferred stock, $0.01 par value, 15,000,000 shares authorized, no shares issued
Common stock, $0.01 par value, 200,000,000 shares authorized, 87,021,935 and 87,152,197 shares issued, respectively	870	872
Paid-in capital	1,975,159	1,970,113
Retained earnings	2,309,429	2,050,034
Accumulated other comprehensive income	1,173	1,189
Total stockholders' equity	4,286,631	4,022,208
Total liabilities and stockholders' equity	$ 8,399,007	$ 7,253,135