Annual report pursuant to Section 13 and 15(d)

Equity Incentive Plans and Stock Based Compensation - Stock Option Activity Under Equity Incentive Plan (Detail)

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Equity Incentive Plans and Stock Based Compensation - Stock Option Activity Under Equity Incentive Plan (Detail) (USD $)
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Schedule Of Stock Option Activity [Line Items]      
Shares Available for Grant, Beginning Balance 1,077,784 765,848 143,505
Shares Available for Grant, Additional shares reserved 1,250,000 1,250,000 2,452,401
Shares Available for Grant, Options granted (1,844,000) (1,196,500) (1,849,500)
Shares Available for Grant, Options exercised         
Shares Available for Grant, Options canceled 14,627 258,436 19,442
Shares Available for Grant, Ending Balance 498,411 1,077,784 765,848
Number of Shares, Beginning Balance 3,672,179 2,745,718 935,660
Number of Shares, Granted 1,844,000 1,196,500 1,849,500
Number of Shares, Exercised (402,580) (11,603) (20,000)
Number of shares, Canceled (14,627) (258,436) (19,442)
Number of Shares, Ending Balance 5,098,972 3,672,179 2,745,718
Weighted Average Exercise Price, Beginning Balance $ 1.45 $ 1.36 $ 1.17
Weighted Average Exercise Price, Additional shares reserved         
Weighted Average Exercise Price, Granted $ 6.24 $ 1.64 $ 1.45
Weighted Average Exercise Price, Exercised $ 1.39 $ 1.24 $ 1.05
Weighted Average Exercise Price, Canceled $ 4.25 $ 1.38 $ 1.61
Weighted Average Exercise Price, Ending Balance $ 3.18 $ 1.45 $ 1.36
Maximum [Member]
      
Schedule Of Stock Option Activity [Line Items]      
Weighted Average Exercise Price, Beginning Balance $ 3.18 $ 3.18 $ 21.66
Weighted Average Exercise Price, Granted $ 7.75 $ 1.86 $ 1.88
Weighted Average Exercise Price, Exercised $ 3.08 $ 1.44 $ 1.30
Weighted Average Exercise Price, Canceled $ 6.18 $ 1.88 $ 1.95
Weighted Average Exercise Price, Ending Balance $ 7.75 $ 3.18 $ 3.18
Minimum [Member]
      
Schedule Of Stock Option Activity [Line Items]      
Weighted Average Exercise Price, Beginning Balance $ 0.42 $ 0.42 $ 0.42
Weighted Average Exercise Price, Granted $ 1.38 $ 1.53 $ 0.99
Weighted Average Exercise Price, Exercised $ 0.79 $ 0.79 $ 0.79
Weighted Average Exercise Price, Canceled $ 0.79 $ 0.79 $ 0.79
Weighted Average Exercise Price, Ending Balance $ 0.42 $ 0.42 $ 0.42