Subsequent Events - Additional Information (Detail) - USD ($)		1 Months Ended		12 Months Ended
	Nov. 18, 2016	Nov. 30, 2016	Aug. 31, 2016	Sep. 30, 2016	Sep. 30, 2014	Nov. 29, 2016
Subsequent Event [Line Items]
Proceeds from the issuance of common stock			$ 43,200,000	$ 52,231,433	$ 172,641,671
Subsequent Event
Subsequent Event [Line Items]
Percentage of workforce reduced due to discontinued clinical program						30.00%
Common Stock Purchase Agreement | Amgen
Subsequent Event [Line Items]
Proceeds from the issuance of common stock				$ 9,000,000
Common Stock Purchase Agreement | Amgen | Subsequent Event
Subsequent Event [Line Items]
Proceeds from the issuance of common stock	$ 12,500,000
Second Tranche | Common Stock Purchase Agreement | Amgen | Subsequent Event
Subsequent Event [Line Items]
Common stock issued	1,745,810
Second Collaboration and License Agreement | Amgen | Subsequent Event
Subsequent Event [Line Items]
Cash received as due under collaboration agreement	$ 30,000,000	$ 30,000,000