CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Statement of Cash Flows [Abstract]
Net (loss) income	$ (10,457,000)	$ 24,443,000
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Amortization of deferred revenue	(4,893,000)	(1,669,000)
Depreciation	1,439,000	937,000
Amortization of intangibles	5,500,000	5,498,000
Inventory write-down	33,000,000	0
Amortization of premium and discount on investments, net	(285,000)	(269,000)
Stock-based compensation to employees	4,039,000	3,526,000
Stock-based compensation to Board of Directors and Scientific Advisory Board	659,000	463,000
Deferred income tax benefit	3,984,000	6,833,000
Retirement plan benefit expense	1,512,000	838,000
Decrease (increase) in assets:
Accounts receivable	4,697,000	(4,843,000)
Inventory	(12,860,000)	(10,069,000)
Other current assets	(417,000)	(6,451,000)
Other assets	80,000	(252,000)
Increase (decrease) in liabilities:
Accounts payable and accrued expenses	826,000	1,914,000
Other current liabilities	(58,000)	417,000
Deferred revenue	48,412,000	3,692,000
Net cash provided by operating activities	75,178,000	25,008,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(3,146,000)	(2,951,000)
Purchases of investments	(267,520,000)	(183,688,000)
Proceeds from sale of investments	263,058,000	175,603,000
Net cash used in investing activities	(7,608,000)	(11,036,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from issuance of common stock under ESPP	171,000	162,000
Repurchase of common stock	0	(7,000,000)
Proceeds from the exercise of common stock options	1,372,000	664,000
Payment of withholding taxes related to stock-based compensation to employees	(5,280,000)	(2,830,000)
Net cash used in financing activities	(3,737,000)	(9,004,000)
INCREASE IN CASH AND CASH EQUIVALENTS	63,833,000	4,968,000
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	45,418,000	70,586,000
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 109,251,000	$ 75,554,000