Financing Arrangements (Details) $ in Thousands, £ in Millions				1 Months Ended		12 Months Ended
	Aug. 11, 2016 USD ($)	Feb. 02, 2016 USD ($)	Jul. 17, 2015 USD ($)	May 31, 2017 USD ($)	Mar. 31, 2013 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2018 GBP (£)	Sep. 30, 2018 USD ($)
Financial arrangement
Long-term debt, gross							$ 200,000			$ 200,000
Less unamortized debt issuance costs							(239)			(207)
Long-term debt							199,761			199,793
Maturities of long-term debt
2019										0
2020										10,700
2021										35,700
2022										35,700
2023										35,700
Amount of interest paid						$ 10,000	14,800	$ 11,000
Short term borrowings
Letters of credit outstanding										41,800
Self-insurance liabilities							$ 7,600			8,600
Letters of credit primarily for self-insured liabilities
Short term borrowings
Letters of Credit and bank guarantees outstanding										8,300
Fair value of instruments										0
Letters of credit and bank guarantees
Short term borrowings
Letters of Credit and bank guarantees outstanding										33,500
United Kingdom
Short term borrowings
Maximum borrowing capacity under credit agreement									£ 20.0	26,100
Borrowings outstanding										$ 0
Senior unsecured notes
Financial arrangement
Interest rate (as a percent)					3.35%
Principal amount of debt instrument					$ 100,000
Short term borrowings
Coupon rate increase based on leverage ratio (as a percent)					0.50%
Series A senior unsecured notes
Financial arrangement
Interest rate (as a percent)							3.35%		3.35%	3.35%
Long-term debt, gross							$ 50,000			$ 50,000
Series B senior unsecured notes
Financial arrangement
Interest rate (as a percent)							3.35%		3.35%	3.35%
Long-term debt, gross							$ 50,000			$ 50,000
Series C senior unsecured notes
Financial arrangement
Interest rate (as a percent)			3.70%				3.70%		3.70%	3.70%
Long-term debt, gross							$ 25,000			$ 25,000
Principal amount of debt instrument			$ 25,000
Short term borrowings
Coupon rate increase based on leverage ratio (as a percent)			0.50%
Series D senior unsecured notes
Financial arrangement
Interest rate (as a percent)		3.93%					3.93%		3.93%	3.93%
Long-term debt, gross							$ 75,000			$ 75,000
Principal amount of debt instrument		$ 75,000
Revolving credit agreement
Short term borrowings
Maximum borrowing capacity under credit agreement										400,000
Borrowings outstanding										0
Letters of credit outstanding										29,000
Available amount under line of credit										371,000
Coupon rate increase based on leverage ratio (as a percent)						0.75%
Cost of debt revision				$ 400
Debt issuance costs incurred	$ 1,300	$ 2,300
Unamortized debt issuance costs										1,900
Revolving credit agreement | United Kingdom
Short term borrowings
Cash on deposit as collateral										17,400
Other revolving credit facilities
Short term borrowings
Letters of credit outstanding										$ 12,800
Letter of credit agreement | United Kingdom
Short term borrowings
Borrowings outstanding								62,700
Cash on deposit as collateral								$ 69,400