Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2019
Liabilities:
Option and purchase right	$ (506)	$ 0
Fair Value, Measurements, Recurring | Quoted Market Prices in Active Markets (Level 1)
Deferred compensation plan assets
Trust Assets	6	16
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets:
Foreign currency forward contracts	305	278
Deferred compensation plan assets
Insurance	18,654	18,684
Liabilities:
Pension plan	(43,981)	(42,948)
Deferred compensation plan liabilities	(19,960)	(21,318)
Long‑term debt	(854,885)	(979,357)
Interest Rate Derivative Liabilities, at Fair Value	(3,258)
Foreign currency forward contracts	(411)	(154)
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Liabilities:
Earn-outs related to acquisitions	(91)	(1,545)
Option and purchase right	(7,167)
Fair Value, Measurements, Recurring | Cash | Quoted Market Prices in Active Markets (Level 1)
Assets:
Defined benefit plan, fair value of plan assets	14,207	14,607
Fair Value, Measurements, Recurring | US Government Agencies Debt Securities
Assets:
Plan assets at net asset value	2,846	4,703
Fair Value, Measurements, Recurring | Liability Driven Investment
Assets:
Plan assets at net asset value	5,603	3,261
Fair Value, Measurements, Recurring | Guernsey Unit Trust
Assets:
Plan assets at net asset value	1,000	997
Fair Value, Measurements, Recurring | Global Absolute Return
Assets:
Plan assets at net asset value	$ 1,935	$ 1,957