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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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.

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Pro forma diluted earnings per share, which is commonly presented in initial public offerings.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Net Income or Loss Available to Common Stockholders plus adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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The weighted average number of shares or units and dilutive common stock or unit equivalents outstanding in the calculation of proforma diluted earnings per share (earnings per unit), which is commonly presented in initial public offerings based on the terms of the offering.

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Adjustment to the weighted average number of basic shares outstanding to convert this to a pro forma presentation.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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