CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 15,886	$ 7,233
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	5,488	4,610
Amortization of intangibles	1,117	1,255
Loss on disposal of property and equipment	30	96
Stock-based compensation expense	6,710	4,407
Amortization of premium (accretion of discount) on marketable securities	154	(110)
Deferred income taxes	1,095	1,161
Decrease in accounts receivable allowance for credit losses	(154)	(180)
Change in operating assets and liabilities:
Accounts receivable	3,831	(9,293)
Inventories	(6,253)	(4,223)
Prepaid expenses and other assets	(3,992)	(4,229)
Accounts payable	8,828	1,220
Taxes payable and accrued liabilities	(6,349)	(871)
Net cash provided by operating activities	26,391	1,076
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(11,603)	(3,459)
Acquisition of technology licenses	0	(214)
Purchases of marketable securities	(16,838)	(4,793)
Proceeds from sales and maturities of marketable securities	15,947	6,787
Net cash used in investing activities	(12,494)	(1,679)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	5,529	4,500
Repurchase of common stock	(2,013)	(7,302)
Payments of dividends to stockholders	(5,644)	(4,937)
Net cash used in financing activities	(2,128)	(7,739)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	11,769	(8,342)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	178,690	134,137
CASH AND CASH EQUIVALENTS AT END OF PERIOD	190,459	125,795
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	5,250	2,533
Unpaid technology licenses	0	100
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for income taxes, net	$ 305	$ 378