CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 219,267	$ 176,712	$ 143,694
Adjustments to reconcile net income to net cash provided by operating activities:
Loss on sale of discontinued business	0	0	255
Stock-based compensation expense	41,090	31,942	20,558
Depreciation of property, plant, and equipment	18,473	13,683	11,678
Amortization of intangible assets	3,076	3,308	3,391
Impairment of intangible assets	0	469	0
Amortization of discounts or premiums on investments	108	205	383
Realized (gain) loss on sale of investments	(501)	(829)	(1,506)
Revaluation of contingent consideration	(3)	(28)	(463)
Change in deferred income taxes	(413)	1,787	(1,908)
Accounts receivable	(1,867)	(55,185)	(13,251)
Unbilled revenue	(906)	(4,604)	(2,308)
Inventories	(16,946)	(37,088)	10,409
Prepaid expenses and other current assets	(9,750)	(7,016)	(5,421)
Accounts payable	(7,247)	12,322	2,087
Accrued expenses	380	14,476	7,771
Accrued income taxes	(21,903)	71,335	1,270
Deferred revenue and customer deposits	1,434	1,619	3,622
Other	(838)	1,215	1,820
Net cash provided by operating activities	223,454	224,323	182,081
Cash flows from investing activities:
Purchases of investments	(782,032)	(636,856)	(751,868)
Maturities and sales of investments	812,565	584,464	657,250
Purchases of property, plant, and equipment	(37,095)	(28,754)	(12,816)
Cash paid for acquisition of business, net of cash acquired	(4,265)	(24,118)	(14,285)
Net cash paid from sale of discontinued business	0	(291)	(113)
Net cash used in investing activities	(10,827)	(105,555)	(121,832)
Cash flows from financing activities:
Issuance of common stock under stock plans	26,783	54,557	43,468
Repurchase of common stock	(203,822)	(123,715)	(47,149)
Payment of dividends	(31,865)	(29,037)	(25,213)
Payment of contingent consideration	(1,000)	(1,926)	(337)
Net cash used in financing activities	(209,904)	(100,121)	(29,231)
Effect of foreign exchange rate changes on cash and cash equivalents	(1,093)	8,294	(3,352)
Net change in cash and cash equivalents	1,630	26,941	27,666
Cash and cash equivalents at beginning of year	106,582	79,641	51,975
Cash and cash equivalents at end of year	$ 108,212	$ 106,582	$ 79,641