CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Statement of Cash Flows [Abstract]
Net (loss) income	$ (3,410,000)	$ 28,728,000
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Amortization of deferred revenue	(7,031,000)	(3,825,000)
Depreciation	2,223,000	1,499,000
Amortization of intangibles	8,249,000	8,248,000
Inventory write-down	33,000,000	0
Amortization of premium and discount on investments, net	(479,000)	(405,000)
Stock-based compensation to employees	6,759,000	5,333,000
Stock-based compensation to Board of Directors and Scientific Advisory Board	818,000	729,000
Deferred income tax benefit	4,291,000	8,737,000
Retirement plan benefit expense	2,433,000	1,257,000
(Increase) decrease in assets:
Accounts receivable	(6,275,000)	(6,450,000)
Inventory	(9,579,000)	(19,239,000)
Other current assets	(167,000)	(6,712,000)
Other assets	193,000	(266,000)
Increase (decrease) in liabilities:
Accounts payable and accrued expenses	1,192,000	(3,119,000)
Other current liabilities	(7,000)	469,000
Deferred revenue	48,411,000	3,793,000
Net cash provided by operating activities	80,621,000	18,777,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(4,650,000)	(4,214,000)
Purchases of investments	(453,672,000)	(301,924,000)
Proceeds from sale of investments	425,660,000	278,226,000
Net cash used in investing activities	(32,662,000)	(27,912,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from issuance of common stock under ESPP	263,000	279,000
Repurchase of common stock	0	(22,500,000)
Proceeds from the exercise of common stock options	1,629,000	1,001,000
Payment of withholding taxes related to stock-based compensation to employees	(5,313,000)	(2,840,000)
Net cash used in financing activities	(3,421,000)	(24,060,000)
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	44,538,000	(33,195,000)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	45,418,000	70,586,000
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 89,956,000	$ 37,391,000