CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 28,001	$ 21,786
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	8,469	8,521
Amortization of intangibles	3,178	3,439
Loss on disposal of property and equipment	38	148
Stock-based compensation expense	11,296	9,428
Amortization of premium on marketable securities	508	429
Deferred income taxes	(648)	225
Increase in accounts receivable allowances	80	193
Change in operating assets and liabilities:
Accounts receivable	(12,249)	(6,252)
Inventories	132	5,185
Prepaid expenses and other assets	(8,349)	(674)
Accounts payable	(3,629)	3,039
Taxes payable and accrued liabilities	3,208	(1,566)
Net cash provided by operating activities	30,035	43,901
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(22,876)	(4,890)
Purchases of marketable securities	(111,574)	(66,211)
Proceeds from maturities of marketable securities	78,140	52,921
Net cash used in investing activities	(56,310)	(18,180)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	5,089	3,448
Repurchase of common stock	0	(6,435)
Payments of dividends to stockholders	(8,299)	(7,483)
Net cash used in financing activities	(3,210)	(10,470)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(29,485)	15,251
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	62,134	90,092
CASH AND CASH EQUIVALENTS AT END OF PERIOD	32,649	105,343
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	5,851	1,140
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid (refund) for income taxes, net	$ (1,775)	$ 4,564