Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Income taxes (Net deferred tax (liabilities) assets) (Details)

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Income taxes (Net deferred tax (liabilities) assets) (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Tax Disclosure [Line Items]      
Deferred tax liabilities, depreciation/impairment $ (1,325,739) $ (1,038,739)  
Deferred tax liabilities, intangibles (9,500) (22,595)  
Deferred tax liabilities, interest expense (166) (588)  
Deferred tax liabilities, accrued maintenance liability (307)    
Deferred tax assets, accrued maintenance liability   6,782  
Deferred tax liabilities, obligations under capital leases and debt obligations (4,691) (3,151)  
Deferred tax liabilities, investments (8,095) (12,641)  
Deferred tax assets, deferred losses on sale of assets 32,119 66,119  
Deferred tax assets, accrued expenses 7,338 13,942  
Valuation allowance (104,858) (127,361) $ (72,000)
Deferred tax assets, losses and credits forward 961,812 805,881  
Deferred tax liabilities, other (70,627) (51,183)  
Net deferred income tax (liabilities) (522,714) (363,534)  
Ireland      
Income Tax Disclosure [Line Items]      
Deferred tax liabilities, depreciation/impairment (1,336,757) (1,030,901)  
Deferred tax liabilities, intangibles (4,159) (6,353)  
Deferred tax liabilities, accrued maintenance liability (4,362) (6,028)  
Deferred tax liabilities, obligations under capital leases and debt obligations (4,691) (3,151)  
Valuation allowance (2,928) (1,562)  
Deferred tax assets, losses and credits forward 850,774 666,214  
Deferred tax liabilities, other (70,042) (46,133)  
Net deferred income tax (liabilities) (572,165) (427,914)  
United States      
Income Tax Disclosure [Line Items]      
Deferred tax liabilities, depreciation/impairment   (16,322)  
Deferred tax assets, depreciation and impairment 1,553    
Deferred tax liabilities, intangibles (5,341) (16,242)  
Deferred tax liabilities, interest expense (166) (588)  
Deferred tax assets, accrued maintenance liability 4,055 12,810  
Deferred tax liabilities, investments (8,095) (12,641)  
Deferred tax assets, deferred losses on sale of assets 32,119 66,119  
Deferred tax assets, accrued expenses 7,338 13,942  
Valuation allowance (59,983) (89,130)  
Deferred tax assets, losses and credits forward 59,260 92,215  
Deferred tax liabilities, other (2,543)    
Deferred tax assets, other   5,539  
Net deferred income tax assets 28,197 55,702  
The Netherlands      
Income Tax Disclosure [Line Items]      
Deferred tax assets, depreciation and impairment 9,138 8,547  
Valuation allowance (18,240) (26,758)  
Deferred tax assets, losses and credits forward 26,047 26,759  
Deferred tax liabilities, other (542) (4,399)  
Net deferred income tax assets 16,403 4,149  
Other      
Income Tax Disclosure [Line Items]      
Deferred tax liabilities, depreciation/impairment   (63)  
Deferred tax assets, depreciation and impairment 327    
Valuation allowance (23,707) (9,911)  
Deferred tax assets, losses and credits forward 25,731 20,693  
Deferred tax liabilities, other   (6,190)  
Deferred tax assets, other 2,500    
Net deferred income tax assets $ 4,851 $ 4,529