Shareholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended							1 Months Ended
	Apr. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Warrants to purchase common stock [Member]	Dec. 31, 2012 Warrants to purchase common stock [Member]	Feb. 29, 2012 Warrants to purchase common stock [Member]	Feb. 29, 2012 Series B convertible preferred stock [Member] Warrants to purchase common stock [Member]	Feb. 29, 2012 IPO [Member]	Feb. 29, 2012 Private placement [Member]
Stockholders Equity [Line Items]
Issuance of common stock	5,750,000								5,175,000
Net proceeds after underwriting discounts, commissions and offering expenses									$ 45,000,000
Gross proceeds in concurrent private placements									12,000,000
Common stock, shares issued		42,865,408		36,354,547						1,200,000
Common stock offering price per share	$ 12.00									$ 10.00
Conversion of preferred stock to common stock									24,332,186
Net proceeds after underwriting discounts, commissions and offering expenses	$ 64,400,000	$ 64,365,000	$ 57,017,000
Warrant common stock exercise price								$ 5.2
Warrant contractual term							10 years
Purchase of warrant common stock		150,000					150,000	159,500
Warrant common stock exercise price							20.00
Warrants outstanding to purchase convertible stock					151,672	301,672
Weighted average exercise price					$ 19.84	$ 12.56