Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities
Net income	$ 36,365	$ 24,286
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	12,749	8,700
Stock-based compensation expense	5,034	3,958
Deferred taxes	1,620	1,608
Gain on sale of businesses	(671)
Amortization of held-to-maturity securities	276	592
Other	7	77
Changes in operating assets and liabilities:
Accounts receivable	(2,648)	(6,914)
Inventories	389	175
Prepaid expenses and other	(1,059)	(775)
Income taxes	133	1,769
Accounts payable	4,408	2,534
Accrued liabilities and other	2,714	3,417
Net cash provided by operating activities	59,317	39,427
Investing activities
Purchases of property and equipment	(43,194)	(13,301)
Cash used for acquisitions, net of cash acquired	(90)
Proceeds from sale of businesses	284
Purchases of marketable securities	(17,129)	(20,037)
Proceeds from maturities of marketable securities	29,056	25,194
Purchases of other assets and investments		(514)
Net cash used in investing activities	(31,073)	(8,658)
Financing activities
Payments on debt	(5,000)
Proceeds from exercises of stock options and other	3,306	3,791
Repurchases of common stock		(4,410)
Net cash used in financing activities	(1,694)	(619)
Effect of exchange rate changes on cash and cash equivalents	(652)	251
Net increase in cash and cash equivalents	25,898	30,401
Cash and cash equivalents, beginning of period	36,707	68,795
Cash and cash equivalents, end of period	$ 62,605	$ 99,196