CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 71,176	$ 193,468	$ 69,984
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	23,743	19,190	18,918
Amortization of intangibles	4,359	5,213	5,267
Loss on disposal of property and equipment	525	249	553
Stock-based compensation expense	30,912	23,347	21,580
Amortization of premium (accretion of discount) on marketable securities	705	(192)	227
Deferred income taxes	(592)	4,019	(4,465)
Increase (decrease) in accounts receivable allowance for credit losses, net	(336)	57	(28)
Change in operating assets and liabilities:
Accounts receivable	(11,300)	(13,259)	5,754
Inventories	(12,498)	(9,523)	(23,770)
Prepaid expenses and other assets	9,153	(2,132)	(1,495)
Accounts payable	5,697	(6,556)	1,336
Taxes payable and accrued liabilities	4,095	10,618	(9,897)
Net cash provided by operating activities	125,639	224,499	83,964
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(70,598)	(24,114)	(24,677)
Proceeds from sale of property and equipment	651	0	0
Acquisition of technology licenses	0	(1,026)	(900)
Purchases of marketable securities	(109,703)	(207,240)	(62,833)
Proceeds from sales and maturities of marketable securities	151,385	70,334	157,551
Net cash provided by (used in) investing activities	(28,265)	(162,046)	69,141
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	10,527	9,908	9,353
Repurchase of common stock	(2,636)	(7,302)	(103,153)
Payments of dividends to stockholders	(25,081)	(20,506)	(18,823)
Proceeds from draw on line of credit	0	0	8,000
Payments on line of credit	0	0	(8,000)
Net cash used in financing activities	(17,190)	(17,900)	(112,623)
NET INCREASE IN CASH AND CASH EQUIVALENTS	80,184	44,553	40,482
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	178,690	134,137	93,655
CASH AND CASH EQUIVALENTS AT END OF PERIOD	258,874	178,690	134,137
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	5,937	4,355	1,818
Unpaid technology licenses	0	0	100
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid (received) for income taxes, net (Note 11)	$ (1,973)	$ 21,327	$ 7,437