Defined Benefit Pension Plan - Fair Value Estimates (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined benefit pension plan
Fair values	$ 26,771	$ 25,779	$ 25,132
Total
Defined benefit pension plan
Fair values	26,771	25,779
Level 1
Defined benefit pension plan
Fair values	94	94
Level 2
Defined benefit pension plan
Fair values	26,677	25,685
Level 3
Defined benefit pension plan
Fair values	0	0
Equity securities | Total
Defined benefit pension plan
Fair values	5,526	5,077
Equity securities | Level 1
Defined benefit pension plan
Fair values	0	0
Equity securities | Level 2
Defined benefit pension plan
Fair values	5,526	5,077
Equity securities | Level 3
Defined benefit pension plan
Fair values	0	0
Corporate bonds | Total
Defined benefit pension plan
Fair values	14,194	14,546
Corporate bonds | Level 1
Defined benefit pension plan
Fair values	0	0
Corporate bonds | Level 2
Defined benefit pension plan
Fair values	14,194	14,546
Corporate bonds | Level 3
Defined benefit pension plan
Fair values	0	0
Diversified fund | Total
Defined benefit pension plan
Fair values	6,957	6,062
Diversified fund | Level 1
Defined benefit pension plan
Fair values	0	0
Diversified fund | Level 2
Defined benefit pension plan
Fair values	6,957	6,062
Diversified fund | Level 3
Defined benefit pension plan
Fair values	0	0
Cash | Total
Defined benefit pension plan
Fair values	94
Cash | Level 1
Defined benefit pension plan
Fair values	94
Cash | Level 2
Defined benefit pension plan
Fair values	0
Cash | Level 3
Defined benefit pension plan
Fair values	$ 0
Cash | Total
Defined benefit pension plan
Fair values		94
Cash | Level 1
Defined benefit pension plan
Fair values		94
Cash | Level 2
Defined benefit pension plan
Fair values		0
Cash | Level 3
Defined benefit pension plan
Fair values		$ 0