CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 18,078	$ 29,581
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	9,431	9,691
Amortization of intangibles	2,483	2,668
Loss on disposal of property and equipment	152	60
Stock-based compensation expense	9,903	11,740
Amortization of premium (accretion of discount) on marketable securities	(230)	376
Deferred income taxes	1,659	(900)
Increase in accounts receivable allowances	57	17
Change in operating assets and liabilities:
Accounts receivable	(14,453)	9,938
Inventories	(8,340)	(11,737)
Prepaid expenses and other assets	(3,614)	(1,388)
Accounts payable	4,153	(7,276)
Taxes payable and accrued liabilities	1,217	(344)
Net cash provided by operating activities	20,496	42,426
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(8,348)	(10,513)
Acquisition of technology licenses	(251)	(500)
Purchases of marketable securities	(54,424)	0
Proceeds from sales and maturities of marketable securities	19,422	90,353
Net cash provided by (used in) investing activities	(43,601)	79,340
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	5,678	5,635
Repurchase of common stock	(7,302)	(63,389)
Payments of dividends to stockholders	(9,917)	(9,480)
Proceeds from draw on line of credit	0	8,000
Payments on line of credit	0	(8,000)
Net cash used in financing activities	(11,541)	(67,234)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(34,646)	54,532
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	134,137	93,655
CASH AND CASH EQUIVALENTS AT END OF PERIOD	99,491	148,187
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	2,098	4,996
Unpaid technology licenses	100	500
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for income taxes, net	$ 890	$ 4,178