Organization - Additional Information (Detail) (USD $)					1 Months Ended		2 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012	Feb. 28, 2014 License Roche	May 31, 2014 Collaborative Arrangement Roche	Jul. 31, 2014 Underwritten Public And Over-Allotment Offering Ordinary Shares
Organization [Line Items]
Accumulated deficit	$ 35,381,000	$ 41,341,000
Cash and cash equivalents	306,153,000	176,677,000	101,859,000	124,860,000
Upfront payment pursuant to License Agreement					30,000,000
Clinical milestone received						15,000,000
Shares sold pursuant to underwritten public offering (in shares)							5,462,500
Net proceeds from issuance of ordinary shares in underwritten public offering							$ 117,400,000