Employee Benefits - Summary of Change in Plan Assets and Benefit Obligation (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Compensation Related Costs [Abstract]
Projected benefit obligation at beginning of year	$ 25,470,000	$ 22,093,000
Service cost	516,000	987,000	$ 873,000
Interest cost	859,000	972,000	826,000
Actuarial (gains) losses	(2,857,000)	2,012,000
Curtailment (Plan Freeze)	(4,579,000)
Benefits paid	(811,000)	(594,000)
Projected benefit obligation at end of year	18,598,000	25,470,000	22,093,000
Fair value of plan assets at beginning of year	19,188,000	17,507,000
Actual return on plan assets	1,986,000	1,644,000
Contributions		631,000
Benefits paid	(811,000)	(594,000)
Fair value of plan assets at end of year	20,363,000	19,188,000	$ 17,507,000
Funded status	$ 1,765,000	$ (6,282,000)