Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 29, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net income	$ 20,477	$ 33,104
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	14,790	12,281
Depreciation of property, plant, and equipment	5,631	5,175
Amortization of intangible assets	1,388	769
Amortization of discounts or premiums on investments	106	(1,461)
Realized (gain) loss on sale of investments	(1,850)	(40)
Reclassification of credit loss on investments	160	0
Revaluation of contingent consideration	0	(985)
Change in deferred income taxes	(1,826)	(1,140)
Accounts receivable	2,182	12,827
Unbilled revenue	(703)	(1,890)
Inventories	4,954	4,073
Prepaid expenses and other current assets	(9,788)	3,191
Accounts payable	(1,613)	4,245
Accrued expenses	12,720	(11,708)
Accrued income taxes	7,650	(3,501)
Deferred revenue and customer deposits	11,961	6,760
Other	(1,097)	(439)
Net cash provided by operating activities	65,142	61,261
Cash flows from investing activities:
Purchases of investments	(199,530)	(258,596)
Maturities and sales of investments	262,126	193,572
Purchases of property, plant, and equipment	(3,074)	(5,078)
Net cash provided by (used in) investing activities	59,522	(70,102)
Cash flows from financing activities:
Issuance of common stock under stock plans	9,971	14,346
Repurchase of common stock	(51,036)	0
Payment of dividends	(9,503)	(8,564)
Net cash provided by (used in) financing activities	(50,568)	5,782
Effect of foreign exchange rate changes on cash and cash equivalents	(6,330)	143
Net change in cash and cash equivalents	67,766	(2,916)
Cash and cash equivalents at beginning of period	171,431	108,212
Cash and cash equivalents at end of period	$ 239,197	$ 105,296