Income Taxes Deferred tax assets and liabilties (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Allowance for Doubtful Accounts	$ 478	$ 291
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities	8,969	6,980
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	677	648
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Self Insurance	25,395	26,000
Deferred Tax Assets, Operating Loss Carryforwards	3,241	682
Deferred Tax Assets, Tax Deferred Expense	4,595	4,846
Deferred Tax Assets, Other	772us-gaap_DeferredTaxAssetsOther	1,207us-gaap_DeferredTaxAssetsOther
Deferred Tax Assets, Gross	44,127us-gaap_DeferredTaxAssetsGross	40,654us-gaap_DeferredTaxAssetsGross
Deferred Tax Assets, Valuation Allowance	0	0
Deferred Tax Assets, Net	44,127us-gaap_DeferredTaxAssetsNet	40,654us-gaap_DeferredTaxAssetsNet
Deferred Tax Liabilities, Property, Plant and Equipment	(125,611)	(85,849)
Deferred Tax Liabilities, Goodwill and Intangible Assets	(2,385)	(1,835)
Deferred Tax Liabilities, Deferred Expense	(2,969)	(741)
Deferred Income Tax Liabilities	(130,965)us-gaap_DeferredIncomeTaxLiabilities	(88,425)us-gaap_DeferredIncomeTaxLiabilities
Deferred Tax Assets (Liabilities), Net	$ (86,838)us-gaap_DeferredTaxAssetsLiabilitiesNet	$ (47,771)us-gaap_DeferredTaxAssetsLiabilitiesNet

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Amount of deferred tax liability attributable to taxable temporary differences.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards, net of deferred tax liability attributable to taxable temporary differences.

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences not separately disclosed.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from reserves and accruals.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from accrued liabilities.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from the allowance for doubtful accounts.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from estimated losses under self insurance.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Amount of deferred tax liability attributable to taxable temporary differences from capitalized costs.

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Amount of deferred tax liability attributable to taxable temporary differences from intangible assets including goodwill.

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