Business, Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended					12 Months Ended				12 Months Ended
	Dec. 31, 2012 Segment	Dec. 31, 2011	Dec. 31, 2010	Oct. 10, 2012 Initial Public Offering	Oct. 10, 2012 Initial Public Offering Convertible Notes Payable	Oct. 10, 2012 Initial Public Offering Convertible Preferred Stock	Oct. 10, 2012 Astra Zeneca	Oct. 23, 2012 Underwriter	Dec. 31, 2012 Minimum	Dec. 31, 2012 Maximum	Oct. 10, 2012 Gsk Convertible Notes	Oct. 10, 2012 Biogen Idec Convertible Notes	Dec. 31, 2012 Licenses Minimum	Dec. 31, 2012 Licenses Maximum	Dec. 31, 2012 Patents
Organization And Summary Of Significant Accounting Policies [Line Items]
Common stock shares, issued				11,250,000			6,250,000	1,480,982
Common stock shares, par value				$ 4.00			$ 4.00	$ 4.00
Proceeds from issuance of common stock	$ 65,788,000			$ 39,500,000			$ 25,000,000	$ 5,500,000
Outstanding principal amount											5,000,000	5,000,000
Accrued interest on convertible notes											788,000	25,000
Common stock issued upon conversion of convertible notes					2,703,269	13,699,999
Underwriting discounts and commissions	3,400,000
Other offering expenses	2,500,000
Stock-based compensation	$ 1,550,000	$ 825,000	$ 603,000
Property and equipment, estimated useful lives									3 years	5 years
Finite lived intangible asset, estimated useful lives													9 years	10 years	10 years
Finite lived intangible asset, weighted average remaining useful life															8 years
Number of operating segments	1