Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Current Assets:
Cash and cash equivalents	$ 102,754	$ 256,965
Short-term investments	176,785	0
Accounts receivable	5,226	3,530
Restricted investments	4,000	7,250
Other current assets	15,906	3,061
Total Current Assets	304,671	270,806
Restricted investments	647	647
Property and equipment, net of accumulated depreciation and amortization of $17,945 and $17,328 as of June 30, 2014 and December 31, 2013, respectively	20,163	15,049
Patent costs, net of accumulated amortization of $1,853 and $1,622 as of June 30, 2014 and December 31, 2013, respectively	5,387	5,042
Other assets	6,441	25
Total Assets	337,309	291,569
Current Liabilities:
Accounts payable	1,309	8,080
Accrued expenses	13,839	14,601
Current portion of long-term debt	96	92
Warrant liability	9,826	9,006
Deferred revenue	3,303	3,299
Other liabilities	1,031	888
Total Current Liabilities	29,404	35,966
Long-term debt	1,525	1,576
Deferred rent and other long-term liabilities	6,459	6,835
Total Liabilities	37,388	44,377
Commitments and contingencies
Stockholders' Equity:
Preferred stock, $.0001 par value, 3,333,333 shares authorized; none issued and outstanding	0	0
Common stock, $.0001 par value, 50,000,000 shares authorized; 40,799,692 and 37,751,920 issued and outstanding as of June 30, 2014 and December 31, 2013, respectively	4	4
Additional paid-in capital	905,335	790,424
Accumulated other comprehensive loss	(35)	0
Accumulated deficit	(605,383)	(543,236)
Total Stockholders' Equity	299,921	247,192
Total Liabilities and Stockholders' Equity	$ 337,309	$ 291,569