Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Apr. 01, 2018	Apr. 02, 2017
Cash flows from operating activities:
Net income	$ 37,217	$ 45,471
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	13,194	7,483
Depreciation of property, plant, and equipment	4,430	3,083
Amortization of intangible assets	769	872
Amortization of discounts or premiums on investments	56	86
Realized (gain) loss on sale of investments	(22)	(65)
Revaluation of contingent consideration	(442)	(275)
Change in deferred income taxes	(1,469)	921
Change in operating assets and liabilities:
Accounts receivable	24,830	(2,238)
Unbilled revenue	3,389	953
Inventories	(27,321)	(5,386)
Prepaid expenses and other current assets	(866)	(12,461)
Accounts payable	5,309	7,167
Accrued expenses	(9,927)	(3,398)
Accrued income taxes	186	397
Deferred revenue and customer deposits	5,877	5,839
Other	(424)	(734)
Net cash provided by operating activities	54,786	47,715
Cash flows from investing activities:
Purchases of investments	(118,108)	(193,612)
Maturities and sales of investments	144,337	171,667
Purchases of property, plant, and equipment	(13,270)	(6,095)
Cash paid for acquisition of business	0	(176)
Cash paid related to discontinued business	0	(291)
Net cash provided by (used in) investing activities	12,959	(28,507)
Cash flows from financing activities:
Issuance of common stock under stock plans	11,123	29,139
Repurchase of common stock	(69,202)	(30,067)
Payment of dividends	(7,787)	(6,497)
Net cash provided by (used in) financing activities	(65,866)	(7,425)
Effect of foreign exchange rate changes on cash and cash equivalents	1,111	1,004
Net change in cash and cash equivalents	2,990	12,787
Cash and cash equivalents at beginning of period	106,582	79,641
Cash and cash equivalents at end of period	$ 109,572	$ 92,428