Goodwill (Details) $ in Thousands	6 Months Ended
	Jul. 04, 2015 USD ($) item	Jun. 28, 2014 USD ($)
Goodwill
Number of reporting units | item	1
Goodwill impairment	$ 0	$ 0
Changes in the carrying amount of goodwill
Balance at the beginning of the period, gross	154,196	153,466
Goodwill adjustments related to acquisitions		1,829
Effect of foreign currency translation	(9)	494
Balance at the end of the period, gross	154,187	155,789
Balance at the beginning of the period, Accumulated impairment losses	(71,893)	(71,893)
Balance at the end of the period, Accumulated impairment losses	(71,893)	(71,893)
Balance at the beginning of the period, net	82,303	81,573
Balance at the end of the period, net	$ 82,294	$ 83,896