Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Changes in the carrying amount of goodwill
Balance at the beginning of the period, Goodwill gross	$ 165,417
Effect of foreign currency translation	527
Balance at the end of the period, Goodwill gross	165,944
Balance at the beginning of the period, Accumulated impairment losses	(76,417)
Balance at the end of the period, Accumulated impairment losses	(76,417)
Balance at the beginning of the period, Goodwill, net	89,000
Balance at the end of the period, Goodwill, net	89,527
Intangible assets impairment losses	$ 0	$ 0