CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 57,872	$ 35,469	$ 26,143
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	15,082	13,736	9,158
Loss on disposal of fixed assets	0	104	17
Share–based compensation expense	10,923	6,970	5,468
Deferred income tax expense (benefit)	3,775	448	(728)
Other charges	34	2	67
Changes in operating assets and liabilities:
Receivables	(311)	825	(6,179)
Inventories	(5,762)	(7,974)	(3,631)
Other assets	(1,895)	76	(2,972)
Accounts payable	1,916	(5,356)	4,336
Accrued payroll and related benefits	4,878	2,795	1,006
Deferred revenue	509	1,864	1,194
Income taxes	(6,643)	1,297	(1,873)
Other accrued expenses and liabilities	(631)	342	(834)
Net cash provided by operating activities	79,747	50,598	31,172
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of short term investments	(38,479)	(19,127)	(16,811)
Proceeds from sales of short term investments	14,571	4,537	24,030
Capital additions	(13,408)	(14,756)	(12,986)
Cash paid for acquisition of a business	0	0	(15,000)
Net cash used in investing activities	(37,316)	(29,346)	(20,767)
CASH FLOWS FROM FINANCING ACTIVITIES:
Exercise of stock options	4,266	2,760	3,182
Employee tax withholdings related to the vesting of equity awards	(4,545)	(2,657)	(2,610)
Excess tax benefits from share-based compensation	0	2,938	3,122
Repurchase of common shares for treasury	(3,485)	0	0
Repurchase and retirement of common shares	(2,285)	0	0
Payment of dividends	(21,351)	(20,861)	(20,504)
Debt issuance costs	0	0	(24)
Net cash used in financing activities	(27,400)	(17,820)	(16,834)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	15,031	3,432	(6,429)
CASH AND CASH EQUIVALENTS, beginning of year	9,623	6,191	12,620
CASH AND CASH EQUIVALENTS, end of year	$ 24,654	$ 9,623	$ 6,191