Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 28, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income	$ 19,335	$ 81,853
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	22,808	23,248
Depreciation of property, plant, and equipment	11,162	10,537
Amortization of intangible assets	2,582	1,538
Intangible asset impairment charges	19,571	0
Excess and obsolete inventory charges	8,783	1,713
Operating lease asset impairment charges	2,534	0
Amortization of discounts or premiums on investments	328	(342)
Realized gain on sale of investments	(2,805)	(422)
Credit loss on investments	75	0
Revaluation of contingent consideration	(114)	(863)
Change in deferred income taxes	1,395	(1,311)
Accounts receivable	(8,957)	11,383
Unbilled revenue	3,804	(1,989)
Inventories	(1,664)	8,681
Prepaid expenses and other current assets	(25,461)	(463)
Accounts payable	143	(4,528)
Accrued expenses	15,806	(12,270)
Accrued income taxes	(25,411)	(4,000)
Deferred revenue and customer deposits	32,586	8,575
Other	2,520	(1,190)
Net cash provided by operating activities	79,020	120,150
Cash flows from investing activities:
Purchases of investments	(317,540)	(664,896)
Maturities and sales of investments	387,765	587,175
Purchases of property, plant, and equipment	(6,985)	(8,969)
Net cash provided by (used in) investing activities	63,240	(86,690)
Cash flows from financing activities:
Issuance of common stock under stock plans	48,235	26,417
Repurchase of common stock	(51,036)	(61,690)
Payment of dividends	(18,972)	(17,146)
Payment of contingent consideration	(1,039)	0
Net cash provided by (used in) financing activities	(22,812)	(52,419)
Effect of foreign exchange rate changes on cash and cash equivalents	(4,858)	(149)
Net change in cash and cash equivalents	114,590	(19,108)
Cash and cash equivalents at beginning of period	171,431	108,212
Cash and cash equivalents at end of period	$ 286,021	$ 89,104