CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 26, 2015	Dec. 27, 2014
Statement of Comprehensive Income [Abstract]
Net loss	$ (6,557)	$ (1,523)	$ (19,185)
Other comprehensive loss, net of tax:
Foreign currency translation adjustments	(2,042)	(397)	(1,502)
Unrealized gains (losses) on available-for-sale marketable securities	29	(64)	(10)
Unrealized gains on derivative instruments	495	0	0
Other comprehensive loss, net of tax	(1,518)	(461)	(1,512)
Comprehensive loss	$ (8,075)	$ (1,984)	$ (20,697)