Financial Instruments - Notional Principal Amounts of Outstanding Derivative Instruments (Details) - USD ($)		9 Months Ended
		Sep. 30, 2019	Dec. 31, 2018
Derivatives Fair Value [Line Items]
Derivative instruments not designated as hedging instruments, description of terms		We typically use forward contracts to reduce the effects of foreign currency exchange rate fluctuations on our cash flows primarily for the Euro versus the U.S. Dollar. Counterparties to our forward contracts consist of major international financial institutions. We monitor our positions and the credit ratings of the counterparties involved and, by policy limits, the amount of credit exposure to any one party. For the three and nine months ended September 30, 2019 and 2018, respectively, our forward contracts have not been designated as hedges and generally had maturities of less than 90 days. We do not use derivatives for trading or speculative purposes.
Not Designated as Hedging Instrument | Foreign Exchange-forward Contracts
Derivatives Fair Value [Line Items]
Foreign currency exchange-forward contracts	[1],[2]	$ 35,000,000	$ 13,000,000

[1] Our derivative contracts address foreign currency exchange fluctuations for the Euro versus the U.S. dollar. The Company had five outstanding derivative contracts as of September 30, 2019 and two outstanding derivative contracts as of December 31, 2018.

[2] The fair value of our outstanding derivatives as of September 30, 2019 was not material and is included in prepaid expenses and other current assets on our unaudited condensed consolidated balance sheets. The fair value of our outstanding derivatives as of December 31, 2018 was not material and is included in accrued expenses and other current liabilities on our unaudited condensed consolidated balance sheets.