CONSOLIDATED BALANCE SHEETS (USD $)
Dec. 31, 2014
Dec. 31, 2013
Current assets:    
Cash and cash equivalents $ 33,901,000 $ 18,889,000
Short-term investments 58,774,000 82,423,000
Restricted cash   86,000
Prepaid expenses and other current assets 2,641,000 557,000
Total current assets 95,316,000 101,955,000
Property and equipment, net 2,825,000 631,000
Long-term investments   22,344,000
Restricted cash 203,000  
Other assets 305,000 331,000
Total assets 98,649,000 125,261,000
Current liabilities:    
Accounts payable 3,216,000 2,760,000
Accrued expenses 5,519,000 4,327,000
Liability classified stock-based compensation awards 469,000 717,000
Total current liabilities 9,204,000 7,804,000
Other liabilities 677,000  
Liability for shares subject to repurchase 2,000 11,000
Stockholders' equity:    
Convertible preferred stock, $0.0001 par value; 5,000 shares authorized, no shares issued and outstanding      
Common stock, $0.0001 par value; 100,000 shares authorized, 25,328 and 27,259 shares issued and outstanding at December 31, 2013 and 2014, respectively 3,000 3,000
Additional paid-in capital 229,770,000 205,068,000
Accumulated other comprehensive income 11,000 28,000
Accumulated deficit (141,018,000) (87,653,000)
Total stockholders' equity 88,766,000 117,446,000
Total liabilities and stockholders' equity $ 98,649,000 $ 125,261,000