CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 46,248	$ 39,798
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	8,408	7,453
Amortization of intangibles	724	1,032
Loss on disposal of property and equipment	75	17
Stock-based compensation expense	9,013	8,480
Amortization of premium on marketable securities	937	176
Deferred income taxes	(936)	1,445
Increase (decrease) in accounts receivable allowance for credit losses	75	(2)
Change in operating assets and liabilities:
Accounts receivable	10,660	(6,345)
Inventories	(3,849)	12,369
Prepaid expenses and other assets	1,552	(3,253)
Accounts payable	(1,709)	3,281
Taxes payable and accrued liabilities	3,399	(6,329)
Net cash provided by operating activities	74,597	58,122
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(14,700)	(11,051)
Proceeds from sale of property and equipment	1,202	25
Purchases of marketable securities	(15,121)	(21,971)
Proceeds from sales and maturities of marketable securities	108,817	63,466
Net cash provided by investing activities	80,198	30,469
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	3,057	3,652
Repurchase of common stock	(134,689)	0
Payments of dividends to stockholders	(10,656)	(7,845)
Net cash used in financing activities	(142,288)	(4,193)
NET INCREASE IN CASH AND CASH EQUIVALENTS	12,507	84,398
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	158,117	258,874
CASH AND CASH EQUIVALENTS AT END OF PERIOD	170,624	343,272
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	5,042	6,116
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for income taxes, net	$ 1,163	$ 1,512