Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flow from operating activities:
Net income	$ 162,151	$ 155,057	$ 52,411
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	73,541	70,667	72,695
Stock-based compensation	51,438	37,616	29,145
Disposal gain on sale of assets	(26,842)	0	0
Tax benefit from deferred income taxes	(12,680)	(11,738)	(5,774)
Changes in operating assets and liabilities (net of effects of acquisitions):
Accounts receivable	(7,193)	8,446	(15,269)
Inventories	(6,773)	(10,642)	10,154
Prepaid expenses and other assets	(7,926)	12,628	1,971
Accounts payable and accrued expenses	4,034	(3,976)	1,584
Deferred revenue	5,579	19,061	1,791
Taxes, accrued compensation, and other current liabilities	(10,924)	(2,539)	75,734
Net cash provided by operating activities	224,405	274,580	224,442
Cash flow from investing activities:
Capital expenditures	(60,857)	(34,659)	(30,256)
Proceeds from sale of assets	32,492	0	0
Capitalization of internally developed software	(9,065)	(14,208)	(41,662)
Additions to other intangibles	(1,209)	(5,399)	(2,384)
Acquisitions of equity-method investments	(13,670)	0	0
Acquisitions, net of cash received	0	(5,534)	0
Purchases of short-term investments	(185,267)	(313,726)	(87,735)
Sales and maturities of short-term investments	219,628	163,530	39,627
Net cash used in investing activities	(17,948)	(209,996)	(122,410)
Cash flow from financing activities:
Principal payments on revolving line of credit	0	0	(25,000)
Proceeds from issuance of common stock	33,191	31,601	29,094
Repurchase of common stock	(171,316)	0	0
Dividends paid	(131,855)	(121,537)	(109,551)
Other	(837)	(907)	(842)
Net cash used in financing activities	(270,817)	(90,843)	(106,299)
Effect of exchange rate changes on cash	(410)	(4,519)	9,148
Net change in cash and cash equivalents	(64,770)	(30,778)	4,881
Cash and cash equivalents at beginning of period	259,386	290,164	285,283
Cash and cash equivalents at end of period	194,616	259,386	290,164
Supplemental disclosures:
Interest paid	0	78	478
Income taxes paid	$ 46,096	$ 32,786	$ 38,033