CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 44,507	$ 34,595
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	13,323	12,670
Amortization of intangibles	4,631	5,051
Loss on disposal of property and equipment	324	216
Stock-based compensation expense	17,822	15,217
Amortization of premium on marketable securities	803	484
Deferred income taxes	(485)	506
Increase in accounts receivable allowances	209	303
Change in operating assets and liabilities:
Accounts receivable	(10,873)	(5,596)
Inventories	(2,594)	1,993
Prepaid expenses and other assets	(21,048)	(2,076)
Accounts payable	5,299	9,037
Taxes payable and accrued liabilities	2,679	(2,241)
Net cash provided by operating activities	54,597	70,159
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(29,567)	(8,074)
Purchases of marketable securities	(146,073)	(122,398)
Proceeds from maturities of marketable securities	120,695	75,128
Net cash used in investing activities	(54,945)	(55,344)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	8,111	8,672
Repurchase of common stock	(6,734)	(6,435)
Payments of dividends to stockholders	(12,463)	(11,254)
Proceeds from Lines of Credit	5,000	0
Repayments of Lines of Credit	(5,000)	0
Net cash used in financing activities	(11,086)	(9,017)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(11,434)	5,798
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	62,134	90,092
CASH AND CASH EQUIVALENTS AT END OF PERIOD	50,700	95,890
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	5,273	891
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid (refund) for income taxes, net	$ (1,593)	$ 4,709