Organization - Additional Information (Detail) (USD $)					1 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2012	Feb. 28, 2014 License Roche	May 31, 2014 Collaborative Arrangement Roche
Organization [Line Items]
Accumulated deficit	$ 22,199,000	$ 41,341,000
Cash and cash equivalents	303,851,000	176,677,000	112,507,000	124,860,000
Upfront payment pursuant to License Agreement					30,000,000
Clinical milestone received						$ 15,000,000