Accounting Changes and Error Corrections Accounting Changes and Error Corrections (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended			12 Months Ended
	Mar. 31, 2014		Mar. 31, 2013	Dec. 31, 2013
Statement of Financial Position [Abstract]
Accounts receivable	$ 73,581			$ 70,897
Deferred tax asset	10,852			10,715
Other current assets	9,726			7,600
Total Current Assets	94,250			92,489
Accumulated depreciation, depletion, and amortization	(3,188,238)			(3,125,282)
Property and Equipment, Net	2,625,067
Total Assets	2,734,902			2,698,505
Accounts payable and accrued liabilities	79,542			82,318
Total Current Liabilities	162,385			176,033
Deferred Tax Liabilities	247,606			241,205
Retained earnings	320,686			315,244
Total Stockholders' Equity	1,075,541			1,065,350
Total Liabilities and Stockholders' Equity	2,734,902			2,698,505
Income Statement [Abstract]
Oil and gas sales	149,057		146,531
Total Revenues	144,180		146,291
General and administrative, net	10,526		12,725
Depreciation, depletion, and amortization	62,651		60,456
Lease operating cost	24,967		26,884
Transportation and gas processing	5,292		4,738
Severance and Other Taxes	9,202		10,025
Total Costs and Expenses	132,473		133,405
Income Before Income Taxes	11,707		12,886
Provision for Income Taxes	6,265		4,848
Net Income	5,442		8,038	(2,442)
Earnings Per Share (Basic)	$ 0.12		$ 0.19
Earnings Per Share (Diluted)	$ 0.12		$ 0.18
Statement of Cash Flows [Abstract]
Deferred income taxes	6,265		4,848
Share-based Compensation	1,784		3,015
Other	(2,862)		(4,161)
(Increase) Decrease in accounts receivable	(2,834)		(5,245)
Increase (decrease) in accounts payable and accrued liabilities	6,288		1,800
Net Cash Provided by Operating Activities	69,699		62,223
Scenario, Previously Reported [Member]
Statement of Financial Position [Abstract]
Accounts receivable	73,082
Deferred tax asset	5,572
Other current assets	10,081
Total Current Assets	88,826
Accumulated depreciation, depletion, and amortization	(3,236,443)
Property and Equipment, Net	2,576,862
Total Assets	2,681,273
Accounts payable and accrued liabilities	81,182
Total Current Liabilities	164,025
Deferred Tax Liabilities	224,230
Retained earnings	288,793
Total Stockholders' Equity	1,043,648
Total Liabilities and Stockholders' Equity	2,681,273
Income Statement [Abstract]
Oil and gas sales	148,558		146,477
Total Revenues	143,681		146,237
General and administrative, net	10,739		12,725
Depreciation, depletion, and amortization	61,685		60,120
Lease operating cost	25,267		27,424
Transportation and gas processing	5,292		6,030
Severance and Other Taxes	9,202		9,775
Total Costs and Expenses	132,020		134,651
Income Before Income Taxes	11,661		11,586
Provision for Income Taxes	6,248		4,377
Net Income	5,413		7,209
Earnings Per Share (Basic)	$ 0.12		$ 0.17
Earnings Per Share (Diluted)	$ 0.12		$ 0.17
Statement of Cash Flows [Abstract]
Deferred income taxes	6,248		4,377
Share-based Compensation	2,054		3,015
Other	(3,216)		(3,864)
(Increase) Decrease in accounts receivable	(2,335)		(5,191)
Increase (decrease) in accounts payable and accrued liabilities	6,885		3,085
Net Cash Provided by Operating Activities	69,699		62,223
Restatement Adjustment [Member]
Statement of Financial Position [Abstract]
Accounts receivable	499
Deferred tax asset	5,280
Other current assets	(355)
Total Current Assets	5,424
Accumulated depreciation, depletion, and amortization	48,205	[1]
Property and Equipment, Net	48,205
Total Assets	53,629
Accounts payable and accrued liabilities	(1,640)
Total Current Liabilities	(1,640)
Deferred Tax Liabilities	23,376	[1]
Retained earnings	31,893	[1]
Total Stockholders' Equity	31,893
Total Liabilities and Stockholders' Equity	53,629
Income Statement [Abstract]
Oil and gas sales	499		54
Total Revenues	499		54
General and administrative, net	(213)		0
Depreciation, depletion, and amortization	966		336
Lease operating cost	(300)		(540)
Transportation and gas processing	0		(1,292)
Severance and Other Taxes	0		250
Total Costs and Expenses	453		(1,246)
Income Before Income Taxes	46		1,300
Provision for Income Taxes	17		471
Net Income	29		829
Earnings Per Share (Basic)	$ 0.00		$ 0.02
Earnings Per Share (Diluted)	$ 0.00		$ 0.01
Statement of Cash Flows [Abstract]
Deferred income taxes	17		471
Share-based Compensation	(270)		0
Other	354		(297)
(Increase) Decrease in accounts receivable	(499)		(54)
Increase (decrease) in accounts payable and accrued liabilities	(597)		(1,285)
Net Cash Provided by Operating Activities	$ 0		$ 0

[1] The adjustments column includes the impact of correcting the error in the ceiling test write-down as of March 31, 2014. Included in these amounts are approximately $49 million related to Accumulated depreciation, depletion, and amortization, $18 million related to the net deferred tax liabilities and $31 million related to retained earnings.