CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 47,248	$ 44,507
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	14,369	13,323
Amortization of intangibles	3,967	4,631
Loss on disposal of property and equipment	455	324
Stock-based compensation expense	16,138	17,822
Amortization of premium on marketable securities	342	803
Deferred income taxes	(1,395)	(485)
Increase in accounts receivable allowances	170	209
Change in operating assets and liabilities:
Accounts receivable	2,886	(10,873)
Inventories	(17,114)	(2,594)
Prepaid expenses and other assets	(2,721)	(21,048)
Accounts payable	2,647	5,299
Taxes payable and accrued liabilities	(1,357)	2,679
Net cash provided by operating activities	65,635	54,597
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(19,120)	(29,567)
Acquisition of technology licenses	(900)	0
Purchases of marketable securities	(58,221)	(146,073)
Proceeds from sales and maturities of marketable securities	147,501	120,695
Net cash provided by (used in) investing activities	69,260	(54,945)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	8,550	8,111
Repurchase of common stock	(74,377)	(6,734)
Payments of dividends to stockholders	(14,172)	(12,463)
Proceeds from draw on line of credit	8,000	5,000
Payments on line of credit	(8,000)	(5,000)
Net cash used in financing activities	(79,999)	(11,086)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	54,896	(11,434)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	93,655	62,134
CASH AND CASH EQUIVALENTS AT END OF PERIOD	148,551	50,700
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	3,424	5,273
Unpaid technology licenses	100	0
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid (refund) for income taxes, net	$ 5,897	$ (1,593)