Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions					1 Months Ended
	Nov. 18, 2016	Sep. 28, 2016	Aug. 08, 2016	Mar. 03, 2015	Nov. 30, 2016	Sep. 30, 2016	Sep. 30, 2015
Class Of Stock [Line Items]
Capital stock authorized for issuance						150,000,000
Common stock, shares authorized						145,000,000	145,000,000
Common stock, par value						$ 0.001	$ 0.001
Preferred stock, shares authorized						5,000,000	5,000,000
Preferred stock, par value						$ 0.001	$ 0.001
Common stock, shares outstanding						69,746,685	59,544,677
Preferred stock, shares outstanding						15,652	15,652
Threshold percentage of common stock ownership upon preferred stock conversion						9.99%
Securities Purchase Agreement
Class Of Stock [Line Items]
Common stock shares sold			7,627,119
Common stock shares sold, price per share			$ 5.90
Aggregate purchase price			$ 45.0
Net proceeds received			$ 43.2
Common Stock Purchase Agreement | Amgen | First Tranche
Class Of Stock [Line Items]
Common stock shares sold		1,256,983
Common stock shares sold, price per share		$ 7.16
Net proceeds received		$ 9.0
Common Stock Purchase Agreement | Amgen | Second Tranche | Subsequent Event
Class Of Stock [Line Items]
Common stock shares sold	1,745,810
Common stock shares sold, price per share	$ 7.16
Net proceeds received					$ 12.5
Novartis
Class Of Stock [Line Items]
Number of shares issued to Novartis				3,321,383
Series C Preferred Stock
Class Of Stock [Line Items]
Common stock, issued upon conversion of preferred stock						2,670,990
Preferred stock, shares outstanding						15,652
2004 Equity Incentive Plan, 2013 Equity Incentive Plan, and Inducement Grants
Class Of Stock [Line Items]
Common Stock, Share reserve for issuance						8,696,623