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Net Income (Loss) Per Share - Additional Information (Detail)
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3 Months Ended | 9 Months Ended | 12 Months Ended | ||
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Sep. 30, 2013
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Sep. 30, 2013
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Sep. 30, 2012
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Dec. 31, 2012
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Dec. 31, 2011
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| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||||
| Antidilutive securities excluded from computation of earnings per share, amount | 3,112,021 | 64,720,563 | 67,342,601 | 59,609,594 | |
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Options [Member]
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| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | |||||
| Antidilutive securities excluded from computation of earnings per share, amount | 60,500 | 2,697,617 | 2,412,575 | 2,313,526 | 3,614,530 |