Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Deferred Tax Liabilities, Net, Noncurrent	$ 20,360	$ 10,929
Current assets
Cash	14,340	6,287
Accounts receivable
Oil and natural gas revenues	31,793	25,823
Joint interest billings	5,554	4,785
Other	1,268	1,066
Derivative instruments	99	19
Deferred Tax Assets, Net	2,806	1,636
Lease and well equipment inventory	923	785
Prepaid expenses	2,195	1,771
Total current assets	58,978	42,172
Oil and natural gas properties, full-cost method
Evaluated	1,198,893	1,090,656
Unproved and unevaluated	222,580	194,306
Other property and equipment	31,464	29,910
Less accumulated depletion, depreciation and amortization	(493,025)	(468,995)
Net property and equipment	959,912	845,877
Other assets
Derivative instruments	267	173
Deferred income taxes		0
Other assets	2,574	2,108
Total other assets	2,841	2,281
Total assets	1,021,731	890,330
Current liabilities
Accounts payable	6,328	25,358
Accrued liabilities	109,158	63,987
Royalties payable	9,395	7,798
Derivative instruments	6,227	2,692
Accrued Income Taxes, Current	1,679	404
Other current liabilities	88	88
Total current liabilities	132,875	100,327
Long-term liabilities
Borrowings under Credit Agreement	270,000	200,000
Asset retirement obligations	9,019	7,309
Other long-term liabilities	3,076	2,588
Total long-term liabilities	302,455	221,079
Commitments and contingencies (Note 9)
Shareholders' equity
Common stock - $0.01 par value, 80,000,000 shares authorized; 67,114,432 and 66,958,867 shares issued; and 65,800,555 and 65,652,690 shares outstanding, respectively	671	670
Additional paid-in capital	550,048	548,935
Retained deficit	46,447	30,084
Treasury stock, at cost, 1,313,877 and 1,306,177 shares, respectively	(10,765)	(10,765)
Total shareholders' equity	586,401	568,924
Total liabilities and shareholders' equity	1,021,731	890,330
Derivative Liability, Noncurrent	$ 0	$ 253