Derivative Instruments - General Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	May 31, 2017	Dec. 31, 2016
Maximum
Managing foreign currency and natural gas exposure
Value of forecasted exposure hedged by derivatives as per management policy (as a percent)	75.00%
Foreign exchange contracts
Managing foreign currency and natural gas exposure
Notional amount of contract	$ 76,681		$ 199,420
Foreign exchange contracts | Maximum
Managing foreign currency and natural gas exposure
Maturity period of derivatives	18 months
Natural gas contracts | Maximum
Managing foreign currency and natural gas exposure
Maturity period of derivatives	24 months
Interest rate swap contract
Managing foreign currency and natural gas exposure
Notional amount of contract	$ 50,000	$ 50,000