Pension Plans - Fair Value of Plan Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	$ 72,063	$ 69,879
Government
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	20,663	26,996
Corporate Investment Grade
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	3,599	4,816
Large Capitalization Stocks
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	23,878	22,648
Commodity Option
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	7,750	1,086
Insurance Company Funds
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	9,131	8,494
Options
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	1,126
Cash
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	5,916	5,839
Level 1
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	62,932	61,385
Level 1 | Government
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	20,663	26,996
Level 1 | Corporate Investment Grade
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	3,599	4,816
Level 1 | Large Capitalization Stocks
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	23,878	22,648
Level 1 | Commodity Option
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	7,750	1,086
Level 1 | Options
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	1,126
Level 1 | Cash
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	5,916	5,839
Level 2
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	9,131	8,494
Level 2 | Insurance Company Funds
Fair Value of Plan Assets [Line Items]
Fair value of plan assets	$ 9,131	$ 8,494