Fair Value Measurements and Derivative Instruments - Balance Sheet Hedging Instruments (Details) - Foreign currency debt - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Derivative Instruments
Carrying value of non-derivative instrument designated as hedging instrument	$ (224,874)	$ 320,152
Current portion of debt
Derivative Instruments
Carrying value of non-derivative instrument designated as hedging instrument	(75,697)	38,168
Long-term debt
Derivative Instruments
Carrying value of non-derivative instrument designated as hedging instrument	$ (149,177)	$ 281,984