CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Statement of Cash Flows [Abstract]
Net income	$ 28,728	$ 16,166
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred revenue	(3,825)	(3,282)
Depreciation	1,499	1,493
Amortization of intangibles	8,248	8,224
Amortization of premium and discount on investments, net	(405)	(336)
Stock-based compensation to employees	5,333	4,514
Stock-based compensation to Board of Directors and Scientific Advisory Board	729	597
Deferred income tax benefit	8,737	0
Retirement plan benefit expense	1,257	1,250
(Increase) decrease in assets:
Accounts receivable	(6,450)	(9,128)
Inventory	(19,239)	3,166
Other current assets	(6,712)	(2,458)
Other assets	(266)	(5)
Increase (decrease) in liabilities:
Accounts payable and accrued expenses	(3,119)	265
Other current liabilities	469	(21)
Deferred revenue	3,793	2,131
Net cash provided by operating activities	18,777	22,576
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(4,214)	(4,200)
Additions to intangibles	0	(367)
Purchases of investments	(301,924)	(284,581)
Proceeds from sale of investments	278,226	255,022
Net cash used in investing activities	(27,912)	(34,126)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from issuance of common stock under ESPP	279	268
Repurchase of common stock	(22,500)	(5,456)
Proceeds from the exercise of common stock options	1,001	890
Payment of withholding taxes related to stock-based compensation to employees	(2,840)	(2,990)
Net cash used in financing activities	(24,060)	(7,288)
DECREASE IN CASH AND CASH EQUIVALENTS	(33,195)	(18,838)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	70,586	85,923
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 37,391	$ 67,085