Stockholders' Equity - Summary of Outstanding Warrant (Detail) (USD $) | 3 Months Ended |
Mar. 31, 2015 | Mar. 31, 2014 |
Warranty Liability [Line Items] | | |
Shares Subject to Outstanding Warrants | $8,327,405 | |
Issuance of common stock to investors (in shares) | 4,600,000 | |
Issuance of common stock in connection with warrant exercises (in shares) | 0 | |
Proceeds from exercise of warrants | 5,375 | 4,841,711 |
12-Oct-11 | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 12-Oct-16 | |
Shares Subject to Outstanding Warrants | 115,314 | |
Exercise Price at End of Period | $3.32 | |
21-Dec-11 | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 21-Dec-16 | |
Shares Subject to Outstanding Warrants | 819,851 | |
Exercise Price at End of Period | $4.88 | |
March 21, 2012; Series B | Series B | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 21-Mar-17 | |
Shares Subject to Outstanding Warrants | 735,900 | |
Exercise Price at End of Period | $4.08 | |
22-Jun-12 | | |
Warranty Liability [Line Items] | | |
Shares Subject to Outstanding Warrants | 572,860 | |
Exercise Price at End of Period | $3.40 | |
25-Jul-12 | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 25-Jul-17 | |
Shares Subject to Outstanding Warrants | 34,888 | |
Exercise Price at End of Period | $3.56 | |
18-Sep-13 | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 18-Mar-19 | |
Shares Subject to Outstanding Warrants | 3,287,192 | |
Exercise Price at End of Period | $2.30 | |
25-Aug-08 | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 25-Aug-15 | |
Shares Subject to Outstanding Warrants | 349,741 | |
Exercise Price at End of Period | $154.40 | |
April 30, 2010 through July 1, 2010 | | |
Warranty Liability [Line Items] | | |
Shares Subject to Outstanding Warrants | 55,473 | |
Exercise Price at End of Period | $72.80 | |
April 30, 2010 through July 1, 2010 | Minimum | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 30-Apr-15 | |
April 30, 2010 through July 1, 2010 | Maximum | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 1-Jul-15 | |
18-Feb-11 | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 18-Feb-16 | |
Shares Subject to Outstanding Warrants | 189,836 | |
Exercise Price at End of Period | $26.28 | |
February 18, 2011; Series B | Series B | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 18-Feb-16 | |
Shares Subject to Outstanding Warrants | 98,481 | |
Exercise Price at End of Period | $24 | |
June 15, 2011, first issue | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 15-Jun-16 | |
Shares Subject to Outstanding Warrants | 361,458 | |
Exercise Price at End of Period | $15.40 | |
June 15, 2011, second issue | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 15-Jun-18 | |
Shares Subject to Outstanding Warrants | 11,250 | |
Exercise Price at End of Period | $12.48 | |
June 15, 2011, third issue | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 15-Jun-18 | |
Shares Subject to Outstanding Warrants | 30,064 | |
Exercise Price at End of Period | $15.40 | |
June 20, 2011, first issue | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 20-Jun-16 | |
Shares Subject to Outstanding Warrants | 14,269 | |
Exercise Price at End of Period | $15.60 | |
June 20, 2011, second issue | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 20-Jun-18 | |
Shares Subject to Outstanding Warrants | 31 | |
Exercise Price at End of Period | $15.60 | |
6-Jul-11 | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 6-Jul-16 | |
Shares Subject to Outstanding Warrants | 104,929 | |
Exercise Price at End of Period | $15.40 | |
23-Aug-11 | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 23-Aug-16 | |
Shares Subject to Outstanding Warrants | 28,750 | |
Exercise Price at End of Period | $15.40 | |
29-Sep-11 | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 29-Sep-16 | |
Shares Subject to Outstanding Warrants | 4,782 | |
Exercise Price at End of Period | $3.32 | |
October 17, 2011 through October 21, 2011 | | |
Warranty Liability [Line Items] | | |
Shares Subject to Outstanding Warrants | 19,138 | |
Exercise Price at End of Period | $10.56 | |
October 17, 2011 through October 21, 2011 | Minimum | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 17-Oct-16 | |
October 17, 2011 through October 21, 2011 | Maximum | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 21-Oct-16 | |
Issuance During Period Eight [Member] | | |
Warranty Liability [Line Items] | | |
Shares Subject to Outstanding Warrants | 9,037 | |
Exercise Price at End of Period | $53.60 | |
Issuance During Period Eight [Member] | Minimum | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 13-Oct-15 | |
Issuance During Period Eight [Member] | Maximum | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 19-Oct-15 | |
19-Jan-12 | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 19-Jan-17 | |
Shares Subject to Outstanding Warrants | 33,187 | |
Exercise Price at End of Period | $4.88 | |
March 20, 2012; Series B | Series B | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 21-Mar-17 | |
Shares Subject to Outstanding Warrants | 1,311,000 | |
Exercise Price at End of Period | $4.08 | |
May 3,2012; Series B | Series B | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 21-Mar-17 | |
Shares Subject to Outstanding Warrants | 27,612 | |
Exercise Price at End of Period | $4.08 | |
June 4, 2012; Series B | Series B | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 21-Mar-17 | |
Shares Subject to Outstanding Warrants | 51,112 | |
Exercise Price at End of Period | $4.08 | |
7-May-12 | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 7-May-19 | |
Shares Subject to Outstanding Warrants | 50,000 | |
Exercise Price at End of Period | $3.60 | |
24-Jan-13 | | |
Warranty Liability [Line Items] | | |
Warrant Expiration Date | 25-Jul-18 | |
Shares Subject to Outstanding Warrants | $11,250 | |
Exercise Price at End of Period | $2.84 | |