Accounting Changes and Error Corrections Accounting Changes and Error Corrections (Details Textual) (USD $)	3 Months Ended			6 Months Ended			12 Months Ended
	Jun. 30, 2014		Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013	Dec. 31, 2013
Property and Equipment, Net	$ 2,661,785,000			$ 2,661,785,000
Retained earnings	327,513,000			327,513,000			315,244,000
Depreciation, Depletion and Amortization	73,090,000		59,773,000	135,741,000		120,229,000
Net Income	6,827,000		7,549,000	12,269,000		15,587,000	(2,442,000)
Provision for Income Taxes	4,934,000		4,762,000	11,199,000		9,610,000
Restatement Adjustment [Member]
Property and Equipment, Net	47,320,000			47,320,000
Retained earnings	30,682,000	[1]		30,682,000	[1]
Depreciation, Depletion and Amortization	885,000		315,000	1,851,000		651,000
Net Income	(1,211,000)		827,000	(1,182,000)		1,656,000
Provision for Income Taxes	(687,000)		469,000	(670,000)		940,000
Ceiling Test Calculation Error Correction [Member] | Restatement Adjustment [Member]
Property and Equipment, Net	48,000,000			48,000,000
Deferred Tax Liabilities, Net	18,000,000			18,000,000
Retained earnings	30,000,000			30,000,000
Depreciation, Depletion and Amortization	800,000		300,000	1,400,000		700,000
Net Income	500,000		200,000	900,000		400,000
Provision for Income Taxes	$ 300,000		$ 100,000	$ 500,000		$ 300,000

[1] The adjustments column includes the impact of correcting the error in the ceiling test write-down as of June 30, 2014. Included in these amounts are approximately $48 million related to Accumulated depreciation, depletion, and amortization, $18 million related to the net deferred tax liabilities and $30 million related to retained earnings.