CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 39,798	$ 15,886
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	7,453	5,488
Amortization of intangibles	1,032	1,117
Loss on disposal of property and equipment	17	30
Stock-based compensation expense	8,480	6,710
Amortization of premium on marketable securities	176	154
Deferred income taxes	1,445	1,095
Decrease in accounts receivable allowance for credit losses	(2)	(154)
Change in operating assets and liabilities:
Accounts receivable	(6,345)	3,831
Inventories	12,369	(6,253)
Prepaid expenses and other assets	(3,253)	(3,992)
Accounts payable	3,281	8,828
Taxes payable and accrued liabilities	(6,329)	(6,349)
Net cash provided by operating activities	58,122	26,391
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(11,051)	(11,603)
Proceeds from sale of property and equipment	25	0
Purchases of marketable securities	(21,971)	(16,838)
Proceeds from sales and maturities of marketable securities	63,466	15,947
Net cash provided by (used in) investing activities	30,469	(12,494)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	3,652	5,529
Repurchase of common stock	0	(2,013)
Payments of dividends to stockholders	(7,845)	(5,644)
Net cash used in financing activities	(4,193)	(2,128)
NET INCREASE IN CASH AND CASH EQUIVALENTS	84,398	11,769
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	258,874	178,690
CASH AND CASH EQUIVALENTS AT END OF PERIOD	343,272	190,459
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	6,116	5,250
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for income taxes, net	$ 1,512	$ 305