Related Party Transaction - Additional Information (Detail)			1 Months Ended
	Jul. 10, 2015 USD ($) $ / shares shares	Oct. 16, 2009 shares	Oct. 31, 2009 Point shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) shares	Mar. 05, 2015 $ / shares
Related Party Transaction [Line Items]
Preferred stock, equivalent ordinary shares upon future consolidation outstanding				32,818,464	32,818,464
Preferred Shares Basis
Related Party Transaction [Line Items]
Share conversion price | $ / shares						$ 0.15
Ordinary Shares Basis
Related Party Transaction [Line Items]
Share conversion price | $ / shares				$ 1.50		$ 1.50
October 2009 Private Placement
Related Party Transaction [Line Items]
Purchase of ADSs (in the form of common stock) by directors in private placement		66,400,000
October 2009 Private Placement | Warrant
Related Party Transaction [Line Items]
Derivative liability | $				$ 0	$ 0
Derivative liability at fair value | $				$ 0
October 2009 Private Placement | American Depositary Shares
Related Party Transaction [Line Items]
Purchase of ADSs (in the form of common stock) by directors in private placement			36,000,000
Number of ADS that can be purchased for each warrant received | Point			0.5
October 2009 Private Placement | American Depositary Shares | Abingworth LLP
Related Party Transaction [Line Items]
Purchase of ADSs (in the form of common stock) by directors in private placement			17,000,000
October 2009 Private Placement | American Depositary Shares | Orbimed Advisors LLC
Related Party Transaction [Line Items]
Purchase of ADSs (in the form of common stock) by directors in private placement			7,000,000
October 2009 Private Placement | American Depositary Shares | Sofinnova Venture Partners VII, LP
Related Party Transaction [Line Items]
Purchase of ADSs (in the form of common stock) by directors in private placement			7,000,000
October 2009 Private Placement | American Depositary Shares | Fountain Healthcare Partners Fund 1, LP
Related Party Transaction [Line Items]
Purchase of ADSs (in the form of common stock) by directors in private placement			5,000,000
Second Private Placement | Series A Preferred Stock
Related Party Transaction [Line Items]
Subscription agreement to purchase Additional shares | $	$ 5,800,000
Second Private Placement | Maximum | Series A Preferred Stock
Related Party Transaction [Line Items]
Preferred stock, equivalent ordinary shares upon future consolidation outstanding	3,886,718
Second Private Placement | American Depositary Shares | Series A Preferred Stock
Related Party Transaction [Line Items]
Purchase of ADSs (in the form of common stock) by directors in private placement	38,867,180
Second Private Placement | Preferred Shares Basis | Series A Preferred Stock
Related Party Transaction [Line Items]
Share conversion price | $ / shares	$ 0.15
Second Private Placement | Ordinary Shares Basis | Series A Preferred Stock
Related Party Transaction [Line Items]
Share conversion price | $ / shares	$ 1.50