Fair Value Measurements (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Apr. 08, 2021	Sep. 30, 2020	Oct. 01, 2019	Sep. 30, 2019
Liabilities:
Unrealized gain	$ 445
Fair Value, Recurring | Fair Value, Inputs, Level 1
Deferred compensation plan assets
Trust Assets	1,251		$ 55
Deferred Compensation Plan Assets, Mutual Funds	17,806
Fair Value, Recurring | Fair Value, Inputs, Level 2
Assets:
Interest Rate Derivative Assets, at Fair Value	3,127
Foreign Currency Contract, Asset, Fair Value Disclosure	24		140
Deferred compensation plan assets
Insurance			19,804
Liabilities:
Pension plan	(46,013)		(47,389)
Deferred compensation plan liabilities	(24,382)		(21,439)
Long‑term debt	(752,988)		(872,441)
Interest Rate Derivative Liabilities, at Fair Value	(303)		(4,669)
Foreign Currency Contracts, Liability, Fair Value Disclosure	(102)		(47)
Fair Value, Recurring | Fair Value, Inputs, Level 2 | Total return swaps—deferred compensation
Liabilities:
Derivative Liability	(130)
Fair Value, Recurring | Fair Value, Inputs, Level 2 | Commodity Contract
Liabilities:
Derivative Liability	(19)
Fair Value, Recurring | Fair Value, Inputs, Level 3
Liabilities:
Open Option Contracts Written, at Fair Value	8,305		7,739
Business Combinations, Earn-out Payments, Fair Value	(150)		(295)		$ (1,545)
Fair Value, Recurring | Cash | Fair Value, Inputs, Level 1
Assets:
Fair value of plan assets	831		15,061
Fair Value, Recurring | US Government Agencies Debt Securities [Member]
Assets:
Plan assets at net asset value	5,158		4,924
Fair Value, Recurring | Liability Driven Investment [Member]
Assets:
Plan assets at net asset value	2,793		3,604
Fair Value, Recurring | Guernsey Unit Trust [Member]
Assets:
Plan assets at net asset value	2,387		1,881
Fair Value, Recurring | Global Absolute Return [Member]
Assets:
Plan assets at net asset value	2,225		2,060
Fair Value, Recurring | Hedge Funds, Multi-strategy
Assets:
Plan assets at net asset value	15,244
Other Current Liabilities | Fair Value, Recurring | Fair Value, Inputs, Level 3
Liabilities:
Business Combinations, Earn-out Payments, Fair Value	(150)		(295)		(611)
Other Noncurrent Liabilities | Fair Value, Recurring | Fair Value, Inputs, Level 3
Liabilities:
Business Combinations, Earn-out Payments, Fair Value	$ 0		0		$ (934)
Frontier
Liabilities:
Open Option Contracts Written, at Fair Value		$ 1,490
Business Acquisition, Percentage Of Voting Interest Remaining				40.00%
Business acquisition, percentage of voting interests acquired	68.00%	8.00%		60.00%
Liabilities, fair value adjustment	$ 2,056
Frontier | Other Current Liabilities
Liabilities:
Open Option Contracts Written, at Fair Value			506
Frontier | Other Noncurrent Liabilities
Liabilities:
Open Option Contracts Written, at Fair Value			$ 6,661