CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 164,413	$ 71,176	$ 193,468
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	31,454	23,743	19,190
Amortization of intangibles	3,494	4,359	5,213
Loss on disposal of property and equipment	3,105	525	249
Stock-based compensation expense	37,609	30,912	23,347
Amortization of premium on marketable securities	1,590	705	(192)
Deferred income taxes	(13,240)	(592)	4,019
Increase (decrease) in accounts receivable allowance for credit losses	18	(336)	57
Change in operating assets and liabilities:
Accounts receivable	(5,501)	(11,300)	(13,259)
Inventories	3,612	(12,498)	(9,523)
Prepaid expenses and other assets	4,326	9,153	(2,132)
Accounts payable	4,067	5,697	(6,556)
Taxes payable and accrued liabilities	(4,079)	4,095	10,618
Net cash provided by operating activities	230,868	125,639	224,499
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(47,272)	(70,598)	(24,114)
Proceeds from sale of property and equipment	35	651	0
Acquisition of technology licenses	0	0	(1,026)
Purchases of marketable securities	(554,018)	(109,703)	(207,240)
Proceeds from sales and maturities of marketable securities	368,457	151,385	70,334
Net cash used in investing activities	(232,798)	(28,265)	(162,046)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	7,710	10,527	9,908
Repurchase of common stock	(73,938)	(2,636)	(7,302)
Payments of dividends to stockholders	(32,599)	(25,081)	(20,506)
Net cash used in financing activities	(98,827)	(17,190)	(17,900)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(100,757)	80,184	44,553
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	258,874	178,690	134,137
CASH AND CASH EQUIVALENTS AT END OF PERIOD	158,117	258,874	178,690
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	10,879	5,937	4,355
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid (received) for income taxes, net	$ 25,644	$ (1,973)	$ 21,327