Summary of Business - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
	Aug. 31, 2013	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Shares issued under initial public offering	5,462,500
Issuance of common stock under IPO to underwriters by selling stockholders	712,500
Public offering price of the shares sold in the offering	$ 12.00
Total gross proceeds from IPO	$ 65,550,000
Aggregate net proceeds received	56,105,000	56,105,000
Accumulated deficit		(95,445,000)	(75,569,000)
Working capital		58,469,000
Cash and cash equivalents		40,775,000	10,006,000	3,877,000	2,215,000
Short-term investments		$ 12,684,000
Reverse Stock Split	1-for-3.138458