Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets
Cash	$ 5,105	$ 2,095
Certificates of deposit	61	230
Accounts receivable
Oil and natural gas revenues	25,193	24,422
Joint interest billings	1,792	4,118
Other	766	974
Derivative instruments	3,978	4,378
Lease and well equipment inventory	597	877
Prepaid expenses	1,318	1,103
Total current assets	38,810	38,197
Oil and natural gas properties, full-cost method
Evaluated	912,618	763,527
Unproved and unevaluated	168,275	149,675
Other property and equipment	28,428	27,258
Less accumulated depletion, depreciation and amortization	(419,066)	(349,370)
Net property and equipment	690,255	591,090
Other assets
Derivative instruments	3,459	771
Deferred income taxes	510	411
Other assets	1,677	1,560
Total other assets	5,646	2,742
Total assets	734,711	632,029
Current liabilities
Accounts payable	35,959	28,120
Accrued liabilities	48,512	59,179
Royalties payable	6,335	6,541
Derivative instruments	257	670
Advances from joint interest owners	0	1,515
Income taxes payable	78
Deferred income taxes	510	411
Other current liabilities	87	56
Total current liabilities	91,738	96,492
Long-term liabilities
Borrowings under Credit Agreement	245,000	150,000
Asset retirement obligations	5,881	5,109
Other long-term liabilities	2,067	1,324
Total long-term liabilities	252,948	156,433
Commitments and contingencies (Note 9)
Shareholders' equity
Common stock - $0.01 par value, 80,000,000 shares authorized; 57,139,755 and 56,778,718 shares issued; and 55,837,912 and 55,577,667 shares outstanding, respectively	571	568
Additional paid-in capital	405,614	404,311
Retained deficit	(5,395)	(15,010)
Treasury stock, at cost, 1,301,843 and 1,201,051 shares, respectively	(10,765)	(10,765)
Total shareholders' equity	390,025	379,104
Total liabilities and shareholders' equity	$ 734,711	$ 632,029