Credit Facilities and Short-term Borrowings (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Apr. 28, 2015
Debt And Line Of Credit Facility [Line Items]
Maximum borrowing capacity	$ 1,017,588
Outstanding borrowings	32,600
Debt financing costs		$ 863	$ 2,359
Foreign Performance Guarantee Facilities [Member]
Debt And Line Of Credit Facility [Line Items]
Maximum borrowing capacity	10,058
Outstanding borrowings	0
Foreign Lines of Credit And Overdraft Facilities [Member]
Debt And Line Of Credit Facility [Line Items]
Maximum borrowing capacity	7,530
Outstanding borrowings	0
Revolving Credit Facility [Member]
Debt And Line Of Credit Facility [Line Items]
Maximum borrowing capacity	$ 1,000,000
Credit facility effective interest rate on outstanding borrowing	2.29%	1.77%
Outstanding borrowings	$ 32,600	$ 156,700
Current portion of outstanding borrowings	32,600	150,000
Debt financing costs			$ 2,359
Balance of unamortized debt issuance costs, line of credit	2,259	3,134
Revolving Credit Agreement [Member]
Debt And Line Of Credit Facility [Line Items]
Maximum borrowing capacity	1,000,000
Option to increase maximum borrowings to this amount	$ 1,200,000
Line of Credit Facility, Expiration Date	Apr. 01, 2020
Variable Rate Basis	LIBOR
Cross default provisions related to the Company’s other outstanding debt arrangements in excess of this amount, the occurrence of which would permit the lenders to accelerate the amounts due thereunder	$ 60,000
Debt Covenant, Minimum Consolidated Net Worth Calculation, Base Value	$ 800,000
Debt Covenant, Minimum Consolidated Net Worth Calculation, Percentage of Net Income	50.00%
Debt Covenant, Minimum Consolidated Net Worth Calculation, Percentage of Net Proceeds of Issuance of Capital Stock	50.00%
Debt Covenant, Leverage Ratio, Maximum	3.5
Debt Covenant, Leverage Ratio During Material Acquisition Period, Maximum	4.0
Debt Covenant, Leverage Ratio Next Two Succeeding Fiscal Quarters Following Material Acquisition, Maximum	3.75
Balance of unamortized debt issuance costs, line of credit	$ 2,259
Third Amended and Restated Credit Agreement [Member]
Debt And Line Of Credit Facility [Line Items]
Balance of unamortized debt issuance costs, line of credit				$ 2,014
Minimum [Member] | Revolving Credit Agreement [Member]
Debt And Line Of Credit Facility [Line Items]
Basis Spread On Variable Rate	0.85%
Maximum [Member] | Revolving Credit Agreement [Member]
Debt And Line Of Credit Facility [Line Items]
Basis Spread On Variable Rate	1.65%
The Notes [Member]
Debt And Line Of Credit Facility [Line Items]
Debt Covenant, Minimum Consolidated Net Worth Calculation, Percentage of Net Income	50.00%
Debt Covenant, Leverage Ratio, Maximum	3.5
Debt Covenant, Leverage Ratio During Material Acquisition Period, Maximum	4.0
Note Purchase Agreements 2008 and 2009 [Member]
Debt And Line Of Credit Facility [Line Items]
Debt Covenant, Minimum Consolidated Net Worth Calculation, Base Value	$ 485,940
Note Purchase Agreement 2013 and 2016 [Member]
Debt And Line Of Credit Facility [Line Items]
Debt Covenant, Minimum Consolidated Net Worth Calculation, Base Value	$ 1,046,619
2016 Note Purchase Agreements [Member]
Debt And Line Of Credit Facility [Line Items]
Debt financing costs		$ 863