CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 7,233	$ 14,200
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	4,610	4,931
Amortization of intangibles	1,255	1,348
Loss on disposal of property and equipment	96	38
Stock-based compensation expense	4,407	5,625
Amortization of premium (accretion of discount) on marketable securities	(110)	262
Deferred income taxes	1,161	(140)
Increase (decrease) in accounts receivable allowances	(180)	5
Change in operating assets and liabilities:
Accounts receivable	(9,293)	(934)
Inventories	(4,223)	(6,121)
Prepaid expenses and other assets	(4,229)	(3,141)
Accounts payable	1,220	233
Taxes payable and accrued liabilities	(871)	(577)
Net cash provided by operating activities	1,076	15,729
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(3,459)	(6,491)
Acquisition of technology licenses	(214)	(500)
Purchases of marketable securities	(4,793)	0
Proceeds from sales and maturities of marketable securities	6,787	52,366
Net cash provided by (used in) investing activities	(1,679)	45,375
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	4,500	4,657
Repurchase of common stock	(7,302)	(33,314)
Payments of dividends to stockholders	(4,937)	(4,775)
Proceeds from draw on line of credit	0	8,000
Payments on line of credit	0	(8,000)
Net cash used in financing activities	(7,739)	(33,432)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(8,342)	27,672
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	134,137	93,655
CASH AND CASH EQUIVALENTS AT END OF PERIOD	125,795	121,327
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	2,533	1,961
Unpaid technology licenses	100	500
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for income taxes, net	$ 378	$ 273