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Summary of Significant Accounting Policies - Insurance Coverage (Details) (USD $)	3 Months Ended
	Mar. 31, 2015 levels	Dec. 31, 2014
Insurance Coverage [Line Items]
Levels of insurance coverage maintained by the Company	3
Amount in excess of primary insurance coverage	$ 150,000,000
Accrual for self-insurance liabilities	6,985,000us-gaap_AccruedInsuranceCurrent	7,490,000us-gaap_AccruedInsuranceCurrent
Other liability policies
Insurance Coverage [Line Items]
Primary limit of insurance coverage	1,000,000
Maritime employer's liability
Insurance Coverage [Line Items]
Primary limit of insurance coverage	10,000,000
Watercraft pollution policy
Insurance Coverage [Line Items]
Primary limit of insurance coverage	$ 5,000,000

Carrying value as of the balance sheet date of obligations incurred through that date and payable to insurance entities to mitigate potential loss from various risks or to satisfy a promise to provide certain coverage's to employees. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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