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Financial Instruments - Derivatives (Details) € in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 EUR (€)
Derivatives, Fair Value [Line Items]
Total long-term debt	$ 2,943,660	$ 2,986,702
Gain (loss) on net investment hedges, gross	45,230	(125,262)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	(9,498)	43,842	$ (18,827)
Gain (loss) on net investment hedges, net of tax	35,732	(81,420)	34,964
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional amount of derivatives	153,873	115,580
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional amount of derivatives	66,906	59,952
Foreign Exchange Forward [Member] \| Designated as Hedging Instrument [Member] \| Prepaid Expenses and Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Fair Value - Asset	1,874	358
Foreign Exchange Forward [Member] \| Designated as Hedging Instrument [Member] \| Other Accrued Expenses [Member]
Derivatives, Fair Value [Line Items]
Fair Value - Liability	$ 1,165	$ 2,243
Note due 2020 [Member]
Derivatives, Fair Value [Line Items]
Face amount of notes \| €				€ 300,000
Gain (loss) on net investment hedges, gross			$ 53,791
Note due 2026 [Member]
Derivatives, Fair Value [Line Items]
Face amount of notes \| €				€ 600,000