Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Earnings Per Share
Net income	$ 27,761	$ 19,949	$ 68,446	$ 51,944
Shares used in computing basic earnings per share (in shares)	43,256	42,553	43,177	42,376
Effect of dilutive securities:
Stock options and other stock-based awards (in shares)	938	821	958	818
Shares used in computing diluted earnings per share (in shares)	44,194	43,374	44,135	43,194
Earnings per share:
Basic (in dollars per share)	$ 0.64	$ 0.47	$ 1.59	$ 1.23
Diluted (in dollars per share)	$ 0.63	$ 0.46	$ 1.55	$ 1.20
Shares attributable to dilutive effect of conversion of debt securities included in computation of diluted earnings per share	200		200