Annual report pursuant to Section 13 and 15(d)

Organization and Description of Business - Additional Information (Detail)

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Organization and Description of Business - Additional Information (Detail) (USD $)
 1 Months Ended 12 Months Ended 90 Months Ended 1 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended
Jul. 31, 2013
Apr. 30, 2013
Oct. 31, 2012
Sep. 30, 2012
Aug. 31, 2012
Jun. 30, 2012
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2013
Jun. 30, 2012
Common Stock [Member]
Dec. 31, 2007
Common Stock [Member]
Feb. 13, 2014
Promissory Note [Member]
Nov. 15, 2011
Series A Convertible Preferred Stock [Member]
Dec. 31, 2010
Series A Convertible Preferred Stock [Member]
Nov. 15, 2011
Series B Convertible Preferred Stock [Member]
Dec. 31, 2011
Series B Convertible Preferred Stock [Member]
Common Stock [Member]
Nov. 15, 2011
Series C Preferred Stock [Member]
Dec. 31, 2011
Series C Preferred Stock [Member]
Dec. 31, 2011
Series C Preferred Stock [Member]
Common Stock [Member]
Dec. 31, 2013
Market Issuance Sales Agreement [Member]
Organization And Nature Of Business [Line Items]                                          
Accumulated deficit             $ (121,342,000) $ (84,184,000)   $ (121,342,000)                      
Public offering of common stock, shares           5,750,000 10,558,422 3,361       2,125,096                 10,558,422
Net proceeds from public offering of common stock           26,400,000 92,399,000 28,855,000 193,000 121,452,000                     89,400,000
Stock Issuance, Maximum Amount Of Proceeds Approved 200,000,000 45,000,000 30,000,000 75,000,000                                  
Conversion of Stock, Shares Converted                           4,357,885   2,525,677   4,612,624 4,612,624    
Proceeds from Issuance of Debt         14,700,000                                
Debt Instrument, Face Amount         15,000,000               15,000,000                
Stock Issued During Period, Shares, Conversion of Convertible Securities                             4,357,885   2,525,677     4,612,624  
Proceeds From Issuance Of Convertible Preferred Stock             0 0 25,784,000 25,784,000         19,400,000            
Proceeds from Issuance or Sale of Equity, Total                     $ 26,400,000                 $ 22,900,000