Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended	12 Months Ended
	Nov. 18, 2016	Sep. 28, 2016	Nov. 30, 2016	Sep. 30, 2017	Mar. 21, 2017	Sep. 30, 2016
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				74,785,426		69,746,685
Preferred stock, shares outstanding				0		15,652
Dividend distribution, declared date				Mar. 21, 2017
Number of rights distributed for each outstanding share of common stock					1
Dividend distribution, record date				Mar. 22, 2017
Rights expiration date				Mar. 21, 2018
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
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
Series C Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares converted				15,652
Common stock, issued upon conversion of preferred stock				2,670,989
Preferred stock, shares outstanding				0
Series D Junior Participating Preferred
Class Of Stock [Line Items]
Preferred stock, par value					$ 0.001
Preferred stock conversion of purchase price per one one thousandth of share					$ 20
Beneficial ownership percentage of common stock upon right exercisable					15.00%
Number of rights distributed for each outstanding share of common stock				1
2004 Equity Incentive Plan, 2013 Equity Incentive Plan, and Inducement Grants
Class Of Stock [Line Items]
Common Stock, Share reserve for issuance				8,902,416