CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 29,581	$ 28,001
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	9,691	8,469
Amortization of intangibles	2,668	3,178
Loss on disposal of property and equipment	60	38
Stock-based compensation expense	11,740	11,296
Amortization of premium on marketable securities	376	508
Deferred income taxes	(900)	(648)
Increase in accounts receivable allowances	17	80
Change in operating assets and liabilities:
Accounts receivable	9,938	(12,249)
Inventories	(11,737)	132
Prepaid expenses and other assets	(1,388)	(8,349)
Accounts payable	(7,276)	(3,629)
Taxes payable and accrued liabilities	(344)	3,208
Net cash provided by operating activities	42,426	30,035
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(10,513)	(22,876)
Acquisition of technology licenses	(500)	0
Purchases of marketable securities	0	(111,574)
Proceeds from sales and maturities of marketable securities	90,353	78,140
Net cash provided by (used in) investing activities	79,340	(56,310)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	5,635	5,089
Repurchase of common stock	(63,389)	0
Payments of dividends to stockholders	(9,480)	(8,299)
Proceeds from draw on line of credit	8,000	0
Payments on line of credit	(8,000)	0
Net cash used in financing activities	(67,234)	(3,210)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	54,532	(29,485)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	93,655	62,134
CASH AND CASH EQUIVALENTS AT END OF PERIOD	148,187	32,649
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	4,996	5,851
Unpaid technology licenses	500	0
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid (refund) for income taxes, net	$ 4,178	$ (1,775)