CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 176,186	$ 203,865	$ 219,267
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	42,661	45,589	41,090
Depreciation of property, plant, and equipment	22,139	21,527	18,473
Gain (Loss) on Disposition of Property Plant Equipment	1,817	324	0
Amortization of intangible assets	4,364	3,373	3,076
Intangible asset impairment charges	19,571	0	0
Excess and Obsolete Inventory Charges	9,908	5,296	2,985
Operating Lease, Impairment Loss	3,427	0	0
Amortization of discounts or premiums on investments	1,274	(618)	108
Realized gain on sale of investments	(4,119)	(1,452)	(501)
Revaluation of contingent consideration	(114)	(1,401)	(3)
Change in deferred income taxes	(3,353)	(94,866)	(413)
Accounts receivable	(21,285)	16,807	(1,867)
Unbilled revenue	(848)	3,530	(906)
Inventories	(10,319)	17,841	(19,931)
Prepaid expenses and other current assets	(9,909)	7,405	(9,750)
Accounts payable	(1,688)	1,633	(7,247)
Accrued expenses	24,542	(8,938)	380
Accrued income taxes	(22,973)	25,266	(21,903)
Deferred revenue and customer deposits	6,571	3,875	1,434
Other	4,548	4,255	(838)
Net cash provided by operating activities	242,400	253,311	223,454
Cash flows from investing activities:
Purchases of investments	(922,867)	(1,031,642)	(782,032)
Maturities and sales of investments	1,104,605	1,062,962	812,565
Purchases of property, plant, and equipment	(13,303)	(21,745)	(37,095)
Business acquisitions	1,004	(166,911)	(4,265)
Net cash provided by (used in) investing activities	169,439	(157,336)	(10,827)
Cash flows from financing activities:
Issuance of common stock under stock plans	125,715	64,581	26,783
Repurchase of common stock	(51,036)	(61,690)	(203,822)
Payment of dividends	(390,508)	(35,124)	(31,865)
Payment of Chiaro contingent consideration	(1,039)	0	(1,000)
Net cash used in financing activities	(316,868)	(32,233)	(209,904)
Effect of foreign exchange rate changes on cash and cash equivalents	2,671	(523)	(1,093)
Net change in cash and cash equivalents	97,642	63,219	1,630
Cash and cash equivalents at beginning of year	171,431	108,212	106,582
Cash and cash equivalents at end of year	$ 269,073	$ 171,431	$ 108,212