Fair Value Measurements (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Inputs, Level 1 [Member]
Deferred compensation plan assets
Trust Assets	$ 16	$ 648
Fair Value, Inputs, Level 2 [Member]
Deferred compensation plan assets
Insurance	18,684	18,448
Interest Rate Derivative Assets, at Fair Value	19
Foreign Currency Contract, Asset, Fair Value Disclosure	278	345
Liabilities:
Pension plan	(42,948)	(35,541)
Deferred compensation plan liabilities	(21,318)	(21,834)
Long‑term debt	(979,357)	(957,441)
Foreign Currency Contracts, Liability, Fair Value Disclosure	154	67
Fair Value, Inputs, Level 3 [Member]
Liabilities:
Earn-outs related to acquisitions	(1,545)	(1,916)	$ (5,995)
Cash | Fair Value, Inputs, Level 1 [Member]
Assets:
Fair value of plan assets	14,607	15,821
US Government Agencies Debt Securities [Member]
Assets:
Plan assets at net asset value	4,703	3,161
Liability Driven Investment [Member]
Assets:
Plan assets at net asset value	3,261	2,598
Guernsey Unit Trust [Member]
Assets:
Plan assets at net asset value	997	965
Global Absolute Return [Member]
Assets:
Plan assets at net asset value	$ 1,957	$ 2,038