CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 123,713	$ 43,898
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	23,400	17,071
Amortization of intangibles	2,699	3,283
Loss on disposal of property and equipment	2,200	311
Stock-based compensation expense	27,325	22,049
Amortization of premium on marketable securities	775	525
Deferred income taxes	(12)	100
Increase in accounts receivable allowance for credit losses	17	155
Change in operating assets and liabilities:
Accounts receivable	(2,979)	(5,328)
Inventories	11,064	(14,425)
Prepaid expenses and other assets	(4,973)	6,133
Accounts payable	6,633	6,365
Taxes payable and accrued liabilities	(6,157)	(864)
Net cash provided by operating activities	183,705	79,273
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(30,305)	(35,738)
Proceeds from sale of property and equipment	35	331
Purchases of marketable securities	(381,903)	(66,066)
Proceeds from sales and maturities of marketable securities	284,036	86,995
Net cash used in investing activities	(128,137)	(14,478)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	7,710	9,662
Repurchase of common stock	(36,165)	(2,636)
Payments of dividends to stockholders	(23,552)	(18,497)
Net cash used in financing activities	(52,007)	(11,471)
NET INCREASE IN CASH AND CASH EQUIVALENTS	3,561	53,324
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	258,874	178,690
CASH AND CASH EQUIVALENTS AT END OF PERIOD	262,435	232,014
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	4,983	14,180
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid (received) for income taxes, net	$ 16,272	$ (1,927)