Derivative Financial Instruments Effect of Derivative Instruments Not Designated as Hedges (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedges amount recognized in earnings	$ 0	$ 0	$ (18,686)
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedges amount recognized in earnings	(5,956)	(3,267)	(18,686)
Currency Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedges amount recognized in earnings	8,400	700
British pound forward contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedges amount recognized in earnings		18,700
Interest (expense)/income | Currency Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedges amount recognized in earnings	(3,505)	0	0
Other (expense)/income, net | Currency Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedges amount recognized in earnings	(2,451)	(3,267)	0
Loss on settlement of foreign currency forward purchase contracts [Member] | British pound forward contracts [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedges amount recognized in earnings	0	0	$ (18,686)
Intercompany GRail Loan [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Foreign Currency Transaction Gain (Loss), Net of Tax	$ (10,800)	$ (3,900)