CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 14,200	$ 14,099
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	4,931	4,112
Amortization of intangibles	1,348	1,612
Loss on disposal of property and equipment	38	38
Stock-based compensation expense	5,625	4,969
Amortization of premium on marketable securities	262	251
Deferred income taxes	(140)	(1,105)
Increase in accounts receivable allowances	5	0
Change in operating assets and liabilities:
Accounts receivable	(934)	(8,518)
Inventories	(6,121)	1,415
Prepaid expenses and other assets	(3,141)	(8,234)
Accounts payable	233	(2,377)
Taxes payable and accrued liabilities	(577)	(315)
Net cash provided by operating activities	15,729	5,947
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(6,491)	(6,403)
Acquisition of technology licenses	(500)	0
Purchases of marketable securities	0	(61,938)
Proceeds from sales and maturities of marketable securities	52,366	46,340
Net cash provided by (used in) investing activities	45,375	(22,001)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	4,657	4,392
Repurchase of common stock	(33,314)	0
Payments of dividends to stockholders	(4,775)	(4,137)
Proceeds from draw on line of credit	8,000	0
Payments on line of credit	(8,000)	0
Net cash provided by (used in) financing activities	(33,432)	255
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	27,672	(15,799)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	93,655	62,134
CASH AND CASH EQUIVALENTS AT END OF PERIOD	121,327	46,335
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	1,961	11,953
Unpaid technology licenses	500	0
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid (refund) for income taxes, net	$ 273	$ (1,439)