Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net income	$ 50,867	$ 63,655	$ 76,588
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	32,594	30,864	26,754
Stock-based compensation expense	14,673	10,781	10,928
Deferred taxes	7,577	6,106	11,936
Gain on sale of businesses	0	0	(671)
Amortization of held-to-maturity securities	415	5	374
Other	(336)	391	(619)
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	(91)	1,848	(6,098)
Inventories	(662)	60	(189)
Prepaid expenses and other	(1,680)	545	(2,098)
Income taxes	(1,960)	6,555	(6,652)
Accounts payable	1,492	(719)	1,942
Accrued liabilities and other	4,080	(4,039)	10,734
Net cash provided by operating activities	106,969	116,052	122,929
Investing activities
Purchases of property, equipment and other capital assets	(47,010)	(62,230)	(87,104)
Cash used for acquisitions, net of cash acquired	0	0	(90)
Proceeds from sale of businesses	0	0	284
Purchases of other assets and investments	(3,000)	(4,000)	(126)
Purchases of marketable securities	(113,200)	(46,403)	(41,384)
Proceeds from maturities of marketable securities	67,737	68,330	65,139
Net cash used in investing activities	(95,473)	(44,303)	(63,281)
Financing activities
Payments on debt	0	0	(5,000)
Principal repayments of finance lease obligations	(154)	0	0
Proceeds from exercises of stock options	7,557	4,391	8,935
Purchases of shares withheld for tax obligations	(3,443)	(2,487)	(2,144)
Repurchases of common stock	(14,686)	(33,521)	(12,229)
Net cash used in financing activities	(10,726)	(31,617)	(10,438)
Effect of exchange rate changes on cash and cash equivalents	1,608	47	(871)
Net increase in cash and cash equivalents	2,378	40,179	48,339
Cash and cash equivalents, beginning of period	125,225	85,046	36,707
Cash and cash equivalents, end of period	127,603	125,225	85,046
Supplemental cash flow disclosure
Cash paid for interest	23	14	39
Cash paid for taxes	$ 5,650	$ 4,002	$ 9,966