Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Oct. 01, 2016	Sep. 30, 2017	Oct. 01, 2016
Net income	$ 19,949	$ 20,018	$ 51,944	$ 41,385
Shares used in computing basic earnings per share (in shares)	42,553,000	41,614,000	42,376,000	41,673,000
Effect of dilutive securities:
Stock options and other stock-based awards (in shares)	821,000	693,000	818,000	590,000
Shares used in computing diluted earnings per share (in shares)	43,374,000	42,307,000	43,194,000	42,263,000
Earnings per share:
Basic (in dollars per share)	$ 0.47	$ 0.48	$ 1.23	$ 0.99
Diluted (in dollars per share)	$ 0.46	$ 0.47	$ 1.20	$ 0.98
Shares excluded from computation of diluted earning per share (in shares)	0	100,000	0	200,000
Shares issued upon conversion of principal amount
Earnings per share:
Shares excluded from computation of diluted earning per share (in shares)			0