Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Oct. 01, 2019
Summary of Accounting and Financial Policies [Line Items]
Adjustment to fair value	$ 0	$ 0	$ 0
Cash and investment restricted as a collateral for outstanding letter of credit	608,000	608,000
Subsequent Event [Member]
Summary of Accounting and Financial Policies [Line Items]
Right-of-use asset				$ 8,300,000
Lease liability				$ 6,800,000
ASU 2016-18 [Member]
Summary of Accounting and Financial Policies [Line Items]
Cash and investment restricted as a collateral for outstanding letter of credit		608,000	$ 608,000
Money Market Funds [Member]
Summary of Accounting and Financial Policies [Line Items]
Cash and investment restricted as a collateral for outstanding letter of credit	$ 608,000	$ 608,000
Maximum [Member]
Summary of Accounting and Financial Policies [Line Items]
Short-term investments maturity period	90 days
Short-term marketable securities maturity period	1 year
Minimum [Member]
Summary of Accounting and Financial Policies [Line Items]
Short-term marketable securities maturity period	90 days
Long-term marketable securities maturity period	1 year
Income tax benefit recognition, percentage of likelihood of being realized upon settlement	50.00%