Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Apr. 04, 2021	Mar. 29, 2020
Cash flows from operating activities:
Net income	$ 69,848	$ 20,477
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	12,009	14,790
Depreciation of property, plant, and equipment	4,259	5,631
Loss (gain) on disposal of property, plant, and equipment	3	2
Amortization of intangible assets	927	1,388
Excess and obsolete inventory charges	705	1,065
Amortization of discounts or premiums on investments	586	106
Realized gain on sale of investments	0	(1,850)
Credit loss on investments	0	160
Change in deferred income taxes	1,250	(1,826)
Accounts receivable	(3,495)	2,182
Unbilled revenue	3,958	(703)
Inventories	(1,323)	3,889
Prepaid expenses and other current assets	(10,882)	(9,788)
Accounts payable	4,760	(1,613)
Accrued expenses	(15,973)	12,720
Accrued income taxes	1,651	7,650
Deferred revenue and customer deposits	30,641	11,961
Other	(285)	(4,206)
Net cash provided by operating activities	98,639	62,035
Cash flows from investing activities:
Purchases of investments	(298,911)	(199,530)
Maturities and sales of investments	160,552	262,126
Purchases of property, plant, and equipment	(2,436)	(3,074)
Net cash provided by (used in) investing activities	(140,795)	59,522
Cash flows from financing activities:
Net proceeds from issuance of common stock under stock plans	34,744	9,971
Repurchase of common stock	(6,479)	(51,036)
Payment of dividends	(10,595)	(9,503)
Net cash provided by (used in) financing activities	17,670	(50,568)
Effect of foreign exchange rate changes on cash and cash equivalents	(1,899)	(3,223)
Net change in cash and cash equivalents	(26,385)	67,766
Cash and cash equivalents at beginning of period	269,073	171,431
Cash and cash equivalents at end of period	$ 242,688	$ 239,197