Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current Assets:
Cash and cash equivalents	$ 74,436	$ 73,551
Short-term investments	91,787	136,793
Accounts receivable	2,416	2,416
Other current assets	24,410	35,036
Total Current Assets	193,049	247,796
Restricted cash and investments	783	782
Property and equipment, net of accumulated depreciation and amortization of $21,037 and $19,896 as of March 31, 2015 and December 31, 2014, respectively	37,759	38,501
Patent costs, net of accumulated amortization of $2,216 and $2,081 as of March 31, 2015 and December 31, 2014, respectively	5,842	5,891
Other assets	5,275	2,063
Total Assets	242,708	295,033
Current Liabilities:
Accounts payable	9,318	12,408
Accrued expenses	15,039	17,366
Current portion of long-term debt	99	98
Current portion of notes payable	4,831	2,492
Deferred revenue	3,363	3,318
Other liabilities	1,256	1,185
Total Current Liabilities	33,906	36,867
Long-term debt	1,450	1,476
Notes payable		2,262
Deferred rent	6,593	6,775
Total Liabilities	41,949	47,380
Commitments and contingencies (Note 9)
Stockholders' Equity:
Preferred stock, $.0001 par value, 3,333,333 shares authorized; none issued and outstanding
Common stock, $.0001 par value, 50,000,000 shares authorized; 41,354,142 and 41,311,512 issued and outstanding at March 31, 2015 and December 31, 2014, respectively	4	4
Additional paid-in capital	941,356	926,769
Accumulated other comprehensive loss	(17)	(95)
Accumulated deficit	(740,584)	(679,025)
Total Stockholders' Equity	200,759	247,653
Total Liabilities and Stockholders' Equity	$ 242,708	$ 295,033