CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 203,865	$ 219,267	$ 176,712
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	45,589	41,090	31,942
Depreciation of property, plant, and equipment	21,527	18,473	13,683
Amortization of intangible assets	3,373	3,076	3,308
Impairment of intangible assets	0	0	469
Amortization of discounts or premiums on investments	(618)	108	205
Realized (gain) loss on sale of investments	(1,452)	(501)	(829)
Revaluation of contingent consideration	(1,401)	(3)	(28)
Change in deferred income taxes	(94,866)	(413)	1,787
Accounts receivable	16,807	(1,867)	(55,185)
Unbilled revenue	3,530	(906)	(4,604)
Inventories	23,137	(16,946)	(37,088)
Prepaid expenses and other current assets	7,405	(9,750)	(7,016)
Accounts payable	1,633	(7,247)	12,322
Accrued expenses	(8,938)	380	14,476
Accrued income taxes	25,266	(21,903)	71,335
Deferred revenue and customer deposits	3,875	1,434	1,619
Other	4,493	(838)	1,215
Net cash provided by operating activities	253,225	223,454	224,323
Cash flows from investing activities:
Purchases of investments	(1,031,642)	(782,032)	(636,856)
Maturities and sales of investments	1,062,962	812,565	584,464
Purchases of property, plant, and equipment	(21,745)	(37,095)	(28,754)
Cash paid for acquisition of business, net of cash acquired	(166,911)	(4,265)	(24,118)
Net cash paid from sale of discontinued business	0	0	(291)
Net cash used in investing activities	(157,336)	(10,827)	(105,555)
Cash flows from financing activities:
Issuance of common stock under stock plans	64,581	26,783	54,557
Repurchase of common stock	(61,690)	(203,822)	(123,715)
Payment of dividends	(35,124)	(31,865)	(29,037)
Payment of contingent consideration	0	(1,000)	(1,926)
Net cash used in financing activities	(32,233)	(209,904)	(100,121)
Effect of foreign exchange rate changes on cash and cash equivalents	(437)	(1,093)	8,294
Net change in cash and cash equivalents	63,219	1,630	26,941
Cash and cash equivalents at beginning of year	108,212	106,582	79,641
Cash and cash equivalents at end of year	$ 171,431	$ 108,212	$ 106,582