Subsequent Event - Additional Information (Detail) - USD ($)	1 Months Ended					12 Months Ended
	Jan. 31, 2016	Mar. 31, 2014	May. 31, 2013	Dec. 31, 2012	Jan. 31, 2011	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Subsequent Event [Line Items]
Net proceeds from sale of common stock		$ 196,800,000	$ 107,900,000			$ 14,547,000	$ 203,851,000	$ 111,682,000
Share of common stock issued		7,360,000	9,200,000	19,000,000	12,565,446
Common stock, par value						$ 0.0001	$ 0.0001
Value of shares purchased by Baker Entities in January 2016 public offering						$ 10,000	$ 10,000
Subsequent Event
Subsequent Event [Line Items]
Net proceeds from sale of common stock	$ 281,600,000
Share of common stock issued	10,344,827
Subsequent Event | Registration Rights Agreement
Subsequent Event [Line Items]
Common stock, par value	$ 0.0001
Expiration period	10 years
Maximum amount of expense agreed to bear under the agreement	$ 50,000
Subsequent Event | Registration Rights Agreement | Baker Brothers Life Sciences L.P.
Subsequent Event [Line Items]
Value of shares purchased by Baker Entities in January 2016 public offering	$ 75,000,000