Derivative Financial Instruments - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Gross notional amount	$ 0	$ 0
Recognized net gains (losses) from derivatives	(11,300,000)	17,900,000	$ 50,300,000
Foreign currency transaction gains (losses) before tax	$ 86,690,000	$ (16,137,000)	$ (22,430,000)