Derivative Financial Instruments Effect of Derivative Instruments Not Designated as Hedges (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedges amount recognized in earnings	$ 0	$ (18,686)	$ 0
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedges amount recognized in earnings	(3,267)	(18,686)	(1,270)
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	3,300
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	0	0	(1,184)
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	(3,267)	0	(86)
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	$ (18,686)	$ 0