CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 35,177	$ 47,248
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	14,262	14,369
Amortization of intangibles	3,840	3,967
Loss on disposal of property and equipment	214	455
Stock-based compensation expense	15,009	16,138
Amortization of premium (accretion of discount) on marketable securities	(296)	342
Deferred income taxes	1,278	(1,395)
Increase in accounts receivable allowances	57	170
Change in operating assets and liabilities:
Accounts receivable	(14,804)	2,886
Inventories	(7,853)	(17,114)
Prepaid expenses and other assets	(3,034)	(2,721)
Accounts payable	(2,636)	2,647
Taxes payable and accrued liabilities	1,126	(1,357)
Net cash provided by operating activities	42,340	65,635
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(14,325)	(19,120)
Acquisition of technology licenses	(351)	(900)
Purchases of marketable securities	(135,288)	(58,221)
Proceeds from sales and maturities of marketable securities	66,184	147,501
Net cash provided by (used in) investing activities	(83,780)	69,260
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	9,683	8,550
Repurchase of common stock	(7,302)	(74,377)
Payments of dividends to stockholders	(14,916)	(14,172)
Proceeds from draw on line of credit	0	8,000
Payments on line of credit	0	(8,000)
Net cash used in financing activities	(12,535)	(79,999)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(53,975)	54,896
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	134,137	93,655
CASH AND CASH EQUIVALENTS AT END OF PERIOD	80,162	148,551
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	2,868	3,424
Unpaid technology licenses	675	100
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for income taxes, net	$ 1,083	$ 5,897