Derivative Financial Instruments and Fair Value Measurements (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 EUR (€)	Dec. 31, 2017 USD ($)
Fair value measured on a recurring basis
Assets
Deferred compensation plan assets	$ 101,600,000		$ 101,600,000			$ 99,100,000
Foreign currency forward contracts	100,000		100,000
Total assets measured at fair value	101,700,000		101,700,000			99,100,000
Liabilities
Foreign currency forward contracts						100,000
Total liabilities measured at fair value						100,000
Fair value measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Deferred compensation plan assets	101,600,000		101,600,000			99,100,000
Foreign currency forward contracts	0		0
Total assets measured at fair value	101,600,000		101,600,000			99,100,000
Liabilities
Foreign currency forward contracts						0
Total liabilities measured at fair value						0
Fair value measured on a recurring basis | Significant Other Observable Inputs (Level 2)
Assets
Deferred compensation plan assets	0		0			0
Foreign currency forward contracts	100,000		100,000
Total assets measured at fair value	100,000		100,000			0
Liabilities
Foreign currency forward contracts						100,000
Total liabilities measured at fair value						100,000
Fair value measured on a recurring basis | Significant Unobservable Inputs (Level 3)
Assets
Deferred compensation plan assets	0		0			0
Foreign currency forward contracts	0		0
Total assets measured at fair value	0		0			0
Liabilities
Foreign currency forward contracts						0
Total liabilities measured at fair value						0
Euro-denominated notes
Net investment hedges [Abstract]
Translation gain (loss) on net investment hedge	(10,000,000)		(10,000,000)			(35,700,000)
Forward contracts | Designated as hedging instrument
Net investment hedges [Abstract]
Translation gain (loss) on net investment hedge	(4,200,000)		(4,200,000)			(4,200,000)
Forward contracts | Not designated as hedging instrument
Net investment hedges [Abstract]
Gain (loss) on derivative	0	$ 0		$ 0
Gain associated with forward contracts included in interest and other expenses			2,000,000
Fair value | Euro-denominated notes | Significant Other Observable Inputs (Level 2)
Liabilities
Carrying value of long-term debt	1,070,000,000		1,070,000,000			939,900,000
Carrying value | Euro-denominated notes
Liabilities
Carrying value of long-term debt	1,036,600,000		1,036,600,000			$ 897,800,000
Notes due September 2022 | Euro-denominated notes | Designated as hedging instrument
Net investment hedges [Abstract]
Long-term debt	462,100,000		462,100,000		€ 400,000,000
Notes due June 2018 | Euro-denominated notes | Designated as hedging instrument
Net investment hedges [Abstract]
Long-term debt	$ 574,500,000		$ 574,500,000		€ 500,000,000