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Aircraft and Property, Plant and Equipment - Additional Information (Narrative) (Details) (USD $)
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0 Months Ended | 3 Months Ended | 12 Months Ended | ||
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Jun. 30, 2014
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Jun. 30, 2014
Aircraft
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Dec. 31, 2014
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Dec. 31, 2013
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Dec. 31, 2012
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| Property, Plant and Equipment [Line Items] | |||||
| Depreciation expense | $ 17,800,000 | $ 13,400,000 | $ 9,000,000 | ||
| Cost of Services, Maintenance Costs | 22,900,000 | 20,000,000 | 15,900,000 | ||
| Sale Leaseback Transaction, Number of Assets Sold | 1 | 1 | |||
| Proceeds from sale-leaseback of aircraft | 24,700,000 | 24,660,000 | 0 | 0 | |
| Sale-leaseback, net book value | 12,300,000 | 12,300,000 | |||
| Lease initial term commencing date | 7 years | ||||
| Lease payment per month | 264,000 | ||||
| Sale-leaseback deferred gain, current | 1,800,000 | ||||
| Sale-leaseback deferred gain, non-current | 9,700,000 | ||||
| Deferred overhauls, net | |||||
| Property, Plant and Equipment [Line Items] | |||||
| Amortization expense | $ 14,700,000 | $ 18,100,000 | $ 12,700,000 | ||