Fair Value Measurements (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017
Quoted Market Prices in Active Markets (Level 1) [Member]
Deferred compensation plan assets
Trust Assets	$ 766	$ 2,146
Significant Other Observable Inputs (Level 2) [Member]
Deferred compensation plan assets
Insurance	18,029	17,396
Liabilities:
Pension plan	(34,162)	(34,803)
Deferred compensation plan liabilities	(21,267)	(21,159)
Long‑term debt	(798,662)	(912,471)
Cash [Member] | Quoted Market Prices in Active Markets (Level 1) [Member]
Assets:
Defined benefit plan, fair value of plan assets	15,703	16,024
US Government Agencies Debt Securities [Member]
Assets:
Plan assets at net asset value	2,938	3,206
Liability Driven Investment [Member]
Assets:
Plan assets at net asset value	3,245	2,754
Guernsey Unit Trust [Member]
Assets:
Plan assets at net asset value	948	932
Global Absolute Return [Member]
Assets:
Plan assets at net asset value	$ 2,058	$ 2,139