Shareholders' Equity - Gains and Losses, Net of Tax Reclassified from Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Location of Gain Reclassified from Accumulated OCI into Income	$ 1,565	$ 4,643
Foreign currency contracts | Other expense, net
Derivative Instruments, Gain (Loss) [Line Items]
Location of Gain Reclassified from Accumulated OCI into Income	1,410	1,325
Foreign currency contracts | Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Location of Gain Reclassified from Accumulated OCI into Income	$ 155	$ 3,318