Accounting Changes and Error Corrections Accounting Changes and Error Corrections (Details Textual) (USD $)	3 Months Ended			12 Months Ended
	Mar. 31, 2014		Mar. 31, 2013	Dec. 31, 2013
Property and Equipment, Net	$ 2,625,067,000
Retained earnings	320,686,000			315,244,000
Depreciation, depletion, and amortization	62,651,000		60,456,000
Net Income	5,442,000		8,038,000	(2,442,000)
Provision for Income Taxes	6,265,000		4,848,000
Restatement Adjustment [Member]
Property and Equipment, Net	48,205,000
Retained earnings	31,893,000	[1]
Depreciation, depletion, and amortization	966,000		336,000
Net Income	29,000		829,000
Provision for Income Taxes	17,000		471,000
Ceiling Test Calculation Error Correction [Member] | Restatement Adjustment [Member]
Property and Equipment, Net	49,000,000
Deferred Tax Liabilities, Net	18,000,000
Retained earnings	31,000,000
Depreciation, depletion, and amortization	700,000		300,000
Net Income	400,000		200,000
Provision for Income Taxes	$ 300,000		$ 100,000

[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.