Condensed Consolidated Balance Sheets (Unaudited) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
ASSETS    
Cash and cash equivalents $ 27,651 $ 19,348
Short-term investments 34,888 21,582
Amounts due under collaboration agreements 3,809 2,892
Prepaid expenses and other current assets 1,903 2,141
Total current assets 68,251 45,963
Property and equipment, net 6,775 6,567
Restricted cash 1,507 1,526
Other assets 9 12
Total 76,542 54,068
Current liabilities:    
Current portion of long-term debt 1,072 1,792
Accounts payable 1,969 1,796
Accrued expenses 4,590 5,260
Current portion of deferred revenue 4,806 5,087
Total current liabilities 12,437 13,935
Long-term liabilities:    
Long-term debt, less current 13,431 1,482
Deferred revenue, less current 338 481
Warrant liability 7,628  
Other long-term liabilities 938 1,006
Total long-term liabilities 22,335 2,969
Total liabilities 34,772 16,904
Stockholders' equity:    
Preferred stock, $0.0001 par value-10,000,000 shares authorized, no shares issued and outstanding at March 31, 2015 and December 31, 2014      
Common stock, $0.0001 par value-200,000,000 shares authorized, 20,393,574 shares issued and outstanding at March 31, 2015, 16,548,681 shares issued and outstanding at December 31, 2014 2 2
Additional paid in capital 190,346 177,269
Accumulated deficit (145,592) (137,279)
Accumulated other comprehensive loss (2,986) (2,828)
Total stockholders' equity 41,770 37,164
Total $ 76,542 $ 54,068