Defined Contribution Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Compensation And Retirement Disclosure [Abstract]
Percentage of employee contributions	50.00%
Percentage of employee eligible compensation	6.00%
Contribution expense	$ 0.3	$ 0.3	$ 0.2

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration