CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 14,099	$ 10,379
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	4,112	4,315
Amortization of intangibles	1,612	1,792
Loss on disposal of property and equipment	38	78
Stock-based compensation expense	4,969	4,416
Amortization of premium on marketable securities	251	260
Deferred income taxes	(1,105)	(81)
Increase in accounts receivable allowances	0	89
Change in operating assets and liabilities:
Accounts receivable	(8,518)	(2,585)
Inventories	1,415	6,269
Prepaid expenses and other assets	(8,234)	(1,388)
Accounts payable	(2,377)	(1,840)
Taxes payable and accrued liabilities	(315)	(1,413)
Net cash provided by operating activities	5,947	20,291
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(6,403)	(2,095)
Purchases of marketable securities	(61,938)	(45,227)
Proceeds from sales and maturities of marketable securities	46,340	38,531
Net cash used in investing activities	(22,001)	(8,791)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	4,392	2,957
Repurchase of common stock	0	(6,085)
Payments of dividends to stockholders	(4,137)	(3,729)
Net cash provided by (used in) financing activities	255	(6,857)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(15,799)	4,643
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	62,134	90,092
CASH AND CASH EQUIVALENTS AT END OF PERIOD	46,335	94,735
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	11,953	1,513
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid (refund) for income taxes, net	$ (1,439)	$ 613