Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 24, 2016	Dec. 31, 2015	Sep. 26, 2015	Dec. 31, 2014
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 31,764	$ 23,626	$ 36,194	$ 48,829
Marketable securities	29,554	49,964
Total cash, cash equivalents and marketable securities	61,318	73,590
Corporate debt securities
Cash and Cash Equivalents [Line Items]
Marketable securities	23,051	35,799
U.S. government agency securities
Cash and Cash Equivalents [Line Items]
Marketable securities	6,503	10,520
Commercial paper
Cash and Cash Equivalents [Line Items]
Marketable securities	0	3,645
Cash
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	17,708	13,378
Money market funds
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 14,056	$ 10,248