Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 03, 2016	Jul. 05, 2015	Jul. 03, 2016	Jul. 05, 2015
Income Statement [Abstract]
Revenue	$ 147,274	$ 143,829	$ 243,479	$ 245,202
Cost of revenue	35,213	30,508	56,181	52,852
Gross margin	112,061	113,321	187,298	192,350
Research, development, and engineering expenses	19,671	18,302	40,226	35,288
Selling, general, and administrative expenses	42,715	43,241	81,053	83,174
Operating income	49,675	51,778	66,019	73,888
Foreign currency gain (loss)	330	(39)	230	620
Investment income	1,447	957	2,584	1,807
Other income (expense)	222	(55)	429	(365)
Income from continuing operations before income tax expense	51,674	52,641	69,262	75,950
Income tax expense on continuing operations	8,660	9,125	11,363	12,962
Net income from continuing operations	43,014	43,516	57,899	62,988
Net income from discontinued operations	(255)	198	(255)	1,228
Net Income	$ 42,759	$ 43,714	$ 57,644	$ 64,216
Basic earnings per weighted-average common and common-equivalent share:
Net income from continuing operations	$ 0.51	$ 0.50	$ 0.68	$ 0.72
Net income (loss) from discontinued operations	(0.01)	0.00	0.00	0.02
Net income	0.50	0.50	0.68	0.74
Diluted earnings per weighted-average common and common-equivalent share:
Net income from continuing operations	0.50	0.49	0.67	0.71
Net income (loss) from discontinued operations	(0.01)	0.00	(0.01)	0.01
Net income	$ 0.49	$ 0.49	$ 0.66	$ 0.72
Weighted-average common and common-equivalent shares outstanding:
Basic	85,107	87,199	85,024	86,977
Diluted	86,806	89,185	86,713	88,951
Cash dividends per common share	$ 0.075	$ 0.07	$ 0.145	$ 0.07