Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Deferred Tax Liabilities, Net, Noncurrent	$ 3,609
Current assets
Cash	6,330	2,095
Certificates of deposit	40	230
Accounts receivable
Oil and natural gas revenues	26,722	24,422
Joint interest billings	2,600	4,118
Other	1,077	974
Derivative instruments	1,037	4,378
Deferred Tax Assets, Net	1,948
Lease and well equipment inventory	687	877
Prepaid expenses	3,250	1,103
Total current assets	43,691	38,197
Oil and natural gas properties, full-cost method
Evaluated	951,736	763,527
Unproved and unevaluated	213,084	149,675
Other property and equipment	29,219	27,258
Less accumulated depletion, depreciation and amortization	(445,193)	(349,370)
Net property and equipment	748,846	591,090
Other assets
Derivative instruments	995	771
Deferred income taxes		411
Other assets	2,288	1,560
Total other assets	3,283	2,742
Total assets	795,820	632,029
Current liabilities
Accounts payable	20,280	28,120
Accrued liabilities	50,048	59,179
Royalties payable	10,352	6,541
Derivative instruments	4,178	670
Advances from joint interest owners	10	1,515
Income taxes payable	980
Deferred income taxes		411
Other current liabilities	87	56
Total current liabilities	85,935	96,492
Long-term liabilities
Borrowings under Credit Agreement	145,000	150,000
Asset retirement obligations	6,147	5,109
Other long-term liabilities	2,463	1,324
Total long-term liabilities	157,219	156,433
Commitments and contingencies (Note 9)
Shareholders' equity
Common stock - $0.01 par value, 80,000,000 shares authorized; 66,927,261 and 56,778,718 shares issued; and 65,625,418 and 55,577,667 shares outstanding, respectively	670	568
Additional paid-in capital	548,051	404,311
Retained deficit	14,710	(15,010)
Treasury stock, at cost, 1,301,843 and 1,201,051 shares, respectively	(10,765)	(10,765)
Total shareholders' equity	552,666	379,104
Total liabilities and shareholders' equity	$ 795,820	$ 632,029