Derivative Instruments - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended		24 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2011 USD ($) instrument	Mar. 31, 2018 EUR (€)	Dec. 31, 2017 EUR (€)
Derivative [Line Items]
Amortization of interest expense			$ 664	$ 659
Amount to be recognized from hedged transactions within 12 months, approximate			6,400
Switzerland
Derivative [Line Items]
Stamp duty expense			2,200
Other (Income) Expense Net
Derivative [Line Items]
Gain (loss) on derivatives		$ 5,100		5,500
Foreign currency transaction gain	$ 300
Foreign currency transaction loss		$ 4,000	900	$ 4,400
4.2% Senior Notes, due December 2021
Derivative [Line Items]
Interest rate on senior notes					4.20%
4.5% Senior Notes, due December 2020
Derivative [Line Items]
Interest rate on senior notes					4.50%
Interest Rate Contract
Derivative [Line Items]
Number of instruments held | instrument					2
Interest Rate Exchange Agreement Expiring 2010 and 2011
Derivative [Line Items]
Amortization of interest expense					$ 68,900
Term of amortized interest expense, years					10 years
Foreign currency exchange contracts
Derivative [Line Items]
Derivative, notional amount | €						€ 180,000,000	€ 180,000,000
Cash received from settlement of contracts			6,600
Foreign currency exchange contracts | Other (Income) Expense Net
Derivative [Line Items]
Gain (loss) on derivatives	$ (300)		$ 900