Collaboration and License Agreements - Amgen, Inc - Additional Information (Detail)					1 Months Ended			12 Months Ended
	Nov. 18, 2016 USD ($) shares	Sep. 30, 2016 Tranche $ / shares shares	Sep. 29, 2016 USD ($) shares	Sep. 28, 2016 USD ($) Agreement	Nov. 30, 2016 USD ($)	Sep. 30, 2016 USD ($) Tranche $ / shares shares	Aug. 31, 2016 USD ($)	Sep. 30, 2016 USD ($) Tranche $ / shares shares	Sep. 30, 2014 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock							$ 43,200,000	$ 52,231,433	$ 172,641,671
Amgen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Stock issued, price per share | $ / shares		$ 7.16				$ 7.16		$ 7.16
Collaboration and License agreements | Amgen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date		Sep. 28, 2016
Number of agreements | Agreement				2
First Collaboration and License Agreement | Amgen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional amount of common stock shares agreed to sell upon exercise of option				$ 5,000,000
Number of trading days, used to calculate share price of Common Stock, surrounding option exercise date				30 days
Cash received as due under collaboration agreement						$ 5,000,000
Collaboration and License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cash to be received as due under collaboration agreement				$ 35,000,000
Collaboration and License agreements | Amgen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock				21,500,000
Collaboration and License agreements | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option payments, and development, regulatory and sales milestone payments.				$ 617,000,000
Second Collaboration and License Agreement | Amgen | Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cash received as due under collaboration agreement	$ 30,000,000				$ 30,000,000
Common Stock Purchase Agreement | Amgen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date		Sep. 28, 2016
Shares issued | shares		3,002,793				3,002,793		3,002,793
Stock issued, price per share | $ / shares		$ 7.16				$ 7.16		$ 7.16
Number of tranches to deliver shares as per agreement | Tranche		2				2		2
Proceeds from the issuance of common stock								$ 9,000,000
Common Stock Purchase Agreement | Amgen | NASDAQ
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of trading days, used to calculate weighted average price of Common Stock, listed in stock market		30 days
Common Stock Purchase Agreement | Amgen | Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock	$ 12,500,000
Common Stock Purchase Agreement Tranche 1 | Amgen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares issued | shares			1,256,983
Proceeds from the issuance of common stock			$ 9,000,000
Common Stock Purchase Agreement Tranche 2 | Amgen | Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares issued | shares	1,745,810
Proceeds from the issuance of common stock	$ 12,500,000