CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 69,984	$ 27,609	$ 48,898
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	18,918	18,374	16,812
Amortization of intangibles	5,267	6,083	6,663
Loss on disposal of property and equipment	553	360	332
Stock-based compensation expense	21,580	24,677	20,885
Amortization of premium on marketable securities	227	1,100	555
Deferred income taxes	(4,465)	15,838	(638)
Increase (decrease) in accounts receivable allowances	(28)	209	207
Change in operating assets and liabilities:
Accounts receivable	5,754	(10,479)	751
Inventories	(23,770)	(4,523)	(630)
Prepaid expenses and other assets	(1,495)	(17,646)	(2,524)
Accounts payable	1,336	396	7,714
Taxes payable and accrued liabilities	(9,897)	20,041	(1,124)
Net cash provided by operating activities	83,964	82,039	97,901
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(24,677)	(32,496)	(12,198)
Acquisition of technology licenses	(900)	0	0
Purchases of marketable securities	(62,833)	(151,663)	(188,654)
Proceeds from sales and maturities of marketable securities	157,551	149,443	83,423
Net cash provided by (used in) investing activities	69,141	(34,716)	(117,429)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	9,353	10,020	13,059
Repurchase of common stock	(103,153)	(9,188)	(6,435)
Payments of dividends to stockholders	(18,823)	(16,634)	(15,054)
Proceeds from draw on line of credit	8,000	5,000	0
Payments on line of credit	(8,000)	(5,000)	0
Net cash used in financing activities	(112,623)	(15,802)	(8,430)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	40,482	31,521	(27,958)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	93,655	62,134	90,092
CASH AND CASH EQUIVALENTS AT END OF PERIOD	134,137	93,655	62,134
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	1,818	4,913	1,825
Unpaid technology licenses	100	0	0
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid (refund) for income taxes, net of refunds (Note 11)	$ 7,437	$ (1,571)	$ 6,613