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Summary of Transactions Involving Warrants (Detail) (Warrant, USD $)
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6 Months Ended |
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Jun. 30, 2012
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Warrant
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| Number of warrants | |
| Balance as of January 1, 2012 | 23,334 |
| Warrants granted | |
| Warrants cancelled | |
| Warrants exercised | |
| Balance as of June 30, 2012 | 23,334 |
| Exercise price range per share | |
| Balance as of January 1, 2012 | $ 4.50 |
| Warrants granted | |
| Warrants cancelled | |
| Warrants exercised | |
| Exercise price range | $ 4.50 |
| Weighted average exercise price per share | |
| Balance as of January 1, 2012 | $ 4.50 |
| Warrants granted | |
| Warrants cancelled | |
| Warrants exercised | |
| Balance as of June 30, 2012 | $ 4.50 |
| Weighted average grant-date fair value per share | |
| Balance as of January 1, 2012 | $ 7.93 |
| Warrants granted | |
| Warrants cancelled | |
| Warrants exercised | |
| Balance as of June 30, 2012 | $ 7.93 |