Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Current assets
Cash	$ 6,287	$ 2,095
Certificates of deposit	0	230
Accounts receivable
Oil and natural gas revenues	25,823	24,422
Joint interest billings	4,785	4,118
Other	1,066	974
Derivative instruments	19	4,378
Deferred income taxes	1,636	0
Lease and well equipment inventory	785	877
Prepaid expenses	1,771	1,103
Total current assets	42,172	38,197
Oil and natural gas properties, full-cost method
Evaluated	1,090,656	763,527
Unproved and unevaluated	194,306	149,675
Other property and equipment	29,910	27,258
Less accumulated depletion, depreciation and amortization	(468,995)	(349,370)
Net property and equipment	845,877	591,090
Other assets
Derivative instruments	173	771
Deferred income taxes	0	411
Other assets	2,108	1,560
Total other assets	2,281	2,742
Total assets	890,330	632,029
Current liabilities
Accounts payable	25,358	28,120
Accrued liabilities	63,987	59,179
Royalties payable	7,798	6,541
Derivative instruments	2,692	670
Advances from joint interest owners	0	1,515
Deferred income taxes	0	411
Income taxes payable	404	0
Other current liabilities	88	56
Total current liabilities	100,327	96,492
Long-term liabilities
Borrowings under Credit Agreement	200,000	150,000
Asset retirement obligations	7,309	5,109
Derivative instruments	253	0
Deferred income taxes	10,929	0
Other long-term liabilities	2,588	1,324
Total long-term liabilities	221,079	156,433
Commitments and contingencies (Note 13)
Shareholders' equity
Common stock — Class A, $0.01 par value, 80,000,000 shares authorized; 66,958,867 and 56,778,718 shares issued; and 65,652,690, and 55,577,667 shares outstanding, respectively	670	568
Additional paid-in capital	548,935	404,311
Retained earnings (deficit)	30,084	(15,010)
Treasury stock, at cost, 1,306,177 and 1,201,051 shares, respectively	(10,765)	(10,765)
Total shareholders' equity	568,924	379,104
Total liabilities and shareholders' equity	$ 890,330	$ 632,029