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Summary of Significant Accounting Policies - Proforma Net Income Per Share (Detail) (USD $) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2013 | Sep. 30, 2012 | Dec. 31, 2012 | Dec. 31, 2011
Net income (loss) used to compute pro forma net income (loss) per common share: |  |  |  |
Basic | $ 0 | $ 0 | $ 0 | $ 0
Diluted | 0 | 0 | 0 | 0
Weighted-average number of common shares, used to calculate net income (loss) per common share: |  |  |  |
Basic | 1,463,798 | 1,078,145 | 1,083,286 | 1,025,602
Diluted | 21,908,859 | 21,412,848 | 1,083,286 | 1,025,602
Weighted-average number of common shares used in calculating pro forma net income (loss) per common share: |  |  |  |
Basic | 18,419,588 |  | 18,039,142 |
Diluted | 20,328,791 |  | 21,473,689 |
Pro forma net income (loss) per common share: |  |  |  |
Basic | $ 0.16 |  | $ 0.38 |
Diluted | $ 0.14 |  | $ 0.38 |
Pro Forma [Member] |  |  |  |
Net income (loss) used to compute pro forma net income (loss) per common share: |  |  |  |
Basic | 2,944,145 |  | 8,361,755 |
Diluted | $ 2,944,145 |  | $ 8,512,450 |
Weighted-average number of common shares, used to calculate net income (loss) per common share: |  |  |  |
Basic | 1,463,798 |  | 1,083,286 |
Diluted | 3,373,001 |  | 4,517,833 |
Add: Pro forma adjustments to reflect assumed weighted-average effect of conversion of convertible preferred stock | 16,955,740 |  | 16,955,740 |
Weighted-average number of common shares used in calculating pro forma net income (loss) per common share: |  |  |  |
Basic | 18,419,588 |  | 18,039,142 |
Diluted | 20,328,791 |  | 21,473,689 |
Pro forma net income (loss) per common share: |  |  |  |
Basic | $ 0.16 |  | $ 0.38 |
Diluted | $ 0.14 |  | $ 0.38 |

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- Definition Pro forma basic earnings per share or earnings per unit, which is commonly presented in initial public offerings based on the terms of the offering. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph b -Subparagraph 7 -Article 11 + Details
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