Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net income	$ 57,302	$ 37,506
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	19,520	13,539
Stock-based compensation expense	7,986	6,159
Deferred taxes	1,770	715
Gain on sale of business	(671)
Amortization of held-to-maturity securities	336	851
Other	160	21
Changes in operating assets and liabilities:
Accounts receivable	(8,993)	(10,679)
Inventories	324	(188)
Prepaid expenses and other	(2,058)	(1,147)
Income taxes	2,278	4,158
Accounts payable	980	1,387
Accrued liabilities and other	6,028	6,678
Net cash provided by operating activities	84,962	59,000
Investing activities
Purchases of property, equipment and other capital assets	(61,898)	(24,164)
Cash used for acquisitions, net of cash acquired	(90)
Proceeds from sale of business	284
Purchases of marketable securities	(41,384)	(20,037)
Proceeds from maturities of marketable securities	44,721	34,090
Purchases of other assets and investments	(126)	(514)
Net cash used in investing activities	(58,493)	(10,625)
Financing activities
Payments on debt	(5,000)
Proceeds from exercises of stock options and other	5,248	5,749
Repurchases of common stock		(4,410)
Net cash provided by financing activities	248	1,339
Effect of exchange rate changes on cash and cash equivalents	(831)	774
Net increase in cash and cash equivalents	25,886	50,488
Cash and cash equivalents, beginning of period	36,707	68,795
Cash and cash equivalents, end of period	$ 62,593	$ 119,283