Derivatives and Hedging Activities - Narrative (Details) $ in Thousands, € in Millions, £ in Millions			3 Months Ended			9 Months Ended
	Feb. 04, 2015 EUR (€)	Feb. 04, 2015 GBP (£)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 EUR (€) € / $ £ / $	Sep. 30, 2016 USD ($) € / $ £ / $	Sep. 30, 2016 GBP (£) € / $ £ / $	Dec. 31, 2015 EUR (€)	Dec. 31, 2015 USD ($)	Dec. 31, 2015 GBP (£)	May 16, 2015 USD ($) $ / € $ / £	Feb. 04, 2015 GBP (£)
Derivative Instruments, Gain (Loss) [Line Items]
Borrowings under credit facility						$ 16,485	$ 476,208
Gain (loss) on derivatives due to ineffectiveness in earnings			$ 300	$ (23)		(200)	(100)
Line of credit, amount drawn									$ 671,023			$ 717,286
Gain on derivative, from partial settlement							19,000
Proceeds from termination of derivatives						0	10,055
Portion of derivative termination proceeds used to repay debt							8,900
Foreign currency derivative instruments, liability fair value									520,600
Net hedge ineffectiveness gain			1,200			5,800
Foreign currency derivative instruments, asset fair value									430,300
Foreign currency derivative instruments, fair value									(90,300)
Gains (losses) on hedging instrument deemed ineffective			1,459	1,505		5,613	2,445
Gains on derivative instruments			375	2,310		3,856	2,785
Fair value of derivatives in net liability position									$ 17,800
GBP
Derivative Instruments, Gain (Loss) [Line Items]
Foreign currency exchange rate								1.30	1.30	1.30				1.58
EUR
Derivative Instruments, Gain (Loss) [Line Items]
Foreign currency exchange rate								1.12	1.12	1.12				1.14
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Remeasurement gains (losses) on non-designated net investment hedges							(2,900)
Gains on derivative instruments			$ 400	2,300		$ 3,900	2,800
Not Designated as Hedging Instrument | Adjustment
Derivative Instruments, Gain (Loss) [Line Items]
Gains recognized in other comprehensive income (loss)				$ 1,100	$ 500		$ 1,100
Cash Flow Hedging | Interest Expense | Interest rate swaps, net (GBP & EUR) | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Estimate of time to transfer (months)						12 months
Estimated amount to be reclassified from OCI						$ 6,000
Revolving Credit Facility
Derivative Instruments, Gain (Loss) [Line Items]
Line of credit, amount drawn	€ 110.5														£ 68.5
Revolving Credit Facility | JPMorgan Chase Bank, N.A.
Derivative Instruments, Gain (Loss) [Line Items]
Borrowings under credit facility	€ 110.5	£ 68.5
Line of credit, amount drawn								€ 278.9	$ 671,000	£ 160.2	€ 288.4	$ 717,300	£ 160.2
Foreign currency derivative instruments, liability fair value								€ 29.4		£ 44.2
Revolving Credit Facility | GBP | Individual Investment | JPMorgan Chase Bank, N.A.
Derivative Instruments, Gain (Loss) [Line Items]
Line of credit, amount drawn									207,800
Revolving Credit Facility | EUR | Individual Investment | JPMorgan Chase Bank, N.A.
Derivative Instruments, Gain (Loss) [Line Items]
Line of credit, amount drawn									$ 312,700
Revolving Credit Facility | Not Designated as Hedging Instrument | GBP | Individual Investment | JPMorgan Chase Bank, N.A.
Derivative Instruments, Gain (Loss) [Line Items]
Line of credit, amount drawn														$ 92,100
Revolving Credit Facility | Not Designated as Hedging Instrument | EUR | Individual Investment | JPMorgan Chase Bank, N.A.
Derivative Instruments, Gain (Loss) [Line Items]
Line of credit, amount drawn														$ 126,000