Retirement Plan - Additional Information (Detail) - 401(k) plan [Member] - USD ($)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan employer discretionary contribution	$ 180,233	$ 158,865	$ 137,608
Defined contribution plan description	Employees are eligible to participate if they are over 21 years of age and have completed a minimum of 1 month of service with 80 hours in that month.
Defined contribution plan employee eligibility age	21 years
Defined contribution plan minimum eligible service months	1 month
Defined contribution plan minimum eligible service hours	80 hours
Defined contribution plan name	401(k) retirement plan
Discretionary Contributions [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan description	To be eligible for the discretionary profit sharing contribution, an employee must be over 21 years of age and have completed a minimum of 6 consecutive months of service with 80 hours of service in each month.
Defined contribution plan employee eligibility age	21 years
Defined contribution plan minimum eligible service months	6 months
Defined contribution plan minimum eligible service hours in each month	80 hours