Pension and Retirement Plans - Accrued benefit liability (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Liability, Defined Benefit Plan [Abstract]
Current accrued benefit liability	$ 335	$ 340
Non-current accrued benefit liability	6,904	6,168
Total accrued benefit liability	7,239	6,508
Accumulated other comprehensive income	6,302	$ 5,298
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year	229
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$ 400