Long-term Debt (Narrative) (Details) € in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2017 EUR (€)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2017 USD ($)	Apr. 28, 2015 USD ($)
Debt Instrument [Line Items]
Debt financing costs			$ 863	$ 2,359
Amortization of debt financing costs recognized as interest expense		$ 1,130	1,165	1,114
Balance of unamortized debt issuance costs			2,091		$ 1,794
Line of Credit Facility, Maximum Borrowing Capacity					1,017,588
Outstanding borrowings					$ 32,600
The Notes [Member]
Debt Instrument [Line Items]
Debt Covenant, Leverage Ratio, Maximum	3.5	3.5
Debt Covenant, Minimum Consolidated Net Worth Calculation, Percentage of Net Income	50.00%				50.00%
Debt Covenant, Calculations, Period Of Time	rolling four quarter basis	rolling four quarter basis
Debt Covenant, Leverage Ratio During Material Acquisition Period, Maximum	4.0	4.0
Prepayment, Maximum Percentage of Principal	100.00%	100.00%
Balance of unamortized debt issuance costs			2,091		$ 1,794
The USD Notes [Member]
Debt Instrument [Line Items]
Debt Covenant, Maximum Percentage of Priority Debt To Consolidated Net Worth	25.00%	25.00%
Prepayment, Partial Payment Minimum		$ 1,000
Non Floating Rate Notes [Member]
Debt Instrument [Line Items]
Prepayment, Make-Whole Amount Computation, Discount Rate Basis Points	50	50
Debt Instrument Prepayment Make Whole Amount Computation	computed by discounting the remaining scheduled payments of interest and principal of the USD Notes being prepaid at a discount rate equal to the sum of 50 basis points and the yield to maturity of U.S. Treasury securities having a maturity equal to the remaining average life of the USD Notes being prepaid	computed by discounting the remaining scheduled payments of interest and principal of the USD Notes being prepaid at a discount rate equal to the sum of 50 basis points and the yield to maturity of U.S. Treasury securities having a maturity equal to the remaining average life of the USD Notes being prepaid
2013 Note Purchase Agreement [Member]
Debt Instrument [Line Items]
Issuance Date	Oct. 01, 2013	Oct. 01, 2013
Face Amount					$ 250,000
Floating Rate Notes [Member]
Debt Instrument [Line Items]
Debt Instrument Prepayment Make Whole Amount Computation	computed as a percentage of the principal amount of the Series J Notes equal to (a) 2%, on or prior to November 15, 2014, (b) 1%, after November 15, 2014 and on or prior to November 15, 2015, and (c) 0% after November 15, 2015	computed as a percentage of the principal amount of the Series J Notes equal to (a) 2%, on or prior to November 15, 2014, (b) 1%, after November 15, 2014 and on or prior to November 15, 2015, and (c) 0% after November 15, 2015
Series J Notes [Member]
Debt Instrument [Line Items]
Variable interest rate	2.60%				2.60%
First Closing Notes [Member]
Debt Instrument [Line Items]
Issuance Date	Oct. 01, 2013	Oct. 01, 2013
Second Closing Notes [Member]
Debt Instrument [Line Items]
Issuance Date	Nov. 15, 2013	Nov. 15, 2013
Note Purchase Agreements 2008 and 2009 [Member]
Debt Instrument [Line Items]
Debt Covenant, Minimum Consolidated Net Worth Calculation, Base Value					$ 485,940
2008 Note Purchase Agreement [Member]
Debt Instrument [Line Items]
Issuance Date	Oct. 01, 2008	Oct. 01, 2008
2009 Note Purchase Agreement [Member]
Debt Instrument [Line Items]
Issuance Date	Apr. 01, 2009	Apr. 01, 2009
2016 Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Issuance Date	Sep. 23, 2016	Sep. 23, 2016
Face Amount | €	€ 160,000
Prepayment, Partial Payment Minimum | €	€ 1,000
Debt financing costs			863
2016 Notes Subject to Swap Agreement [Member]
Debt Instrument [Line Items]
Debt Instrument Prepayment Make Whole Amount Computation	adjusted for theoretical holder returns foregone on hypothetical reinvestments in U.S. Treasury securities (the "Swapped Notes") is equal to the excess of an amount equal to the remaining scheduled payments to be paid in respect of such called principal under such swap agreement discounted at a rate equal to 50 basis points and the yield to maturity of U.S. Treasury securities having a maturity equal to the remaining average life of the Swapped Notes being prepaid over the amount of payments in U.S. dollars that would be paid to the holder of the Swapped Note in respect of the called principal under the swap agreement, which amount will be increased or reduced, as applicable, in an amount equal to any net gain or loss realized by the holder of such Swapped Note on swap transactions under such swap agreement as a result of such prepayment	adjusted for theoretical holder returns foregone on hypothetical reinvestments in U.S. Treasury securities (the "Swapped Notes") is equal to the excess of an amount equal to the remaining scheduled payments to be paid in respect of such called principal under such swap agreement discounted at a rate equal to 50 basis points and the yield to maturity of U.S. Treasury securities having a maturity equal to the remaining average life of the Swapped Notes being prepaid over the amount of payments in U.S. dollars that would be paid to the holder of the Swapped Note in respect of the called principal under the swap agreement, which amount will be increased or reduced, as applicable, in an amount equal to any net gain or loss realized by the holder of such Swapped Note on swap transactions under such swap agreement as a result of such prepayment
2016 Notes Not Subject to Swap Agreement [Member]
Debt Instrument [Line Items]
Debt Instrument Prepayment Make Whole Amount Computation	computed by discounting the remaining scheduled payments of interest and principal of such notes being prepaid at a discount rate equal to the sum of 50 basis points and the yield to maturity of the German Bund having a maturity equal to the remaining average life of the 2016 Notes being prepaid	computed by discounting the remaining scheduled payments of interest and principal of such notes being prepaid at a discount rate equal to the sum of 50 basis points and the yield to maturity of the German Bund having a maturity equal to the remaining average life of the 2016 Notes being prepaid
Series M Notes [Member]
Debt Instrument [Line Items]
Face Amount | €	€ 40,000
Series N Notes [Member]
Debt Instrument [Line Items]
Face Amount | €	77,000
Series O Notes [Member]
Debt Instrument [Line Items]
Face Amount | €	€ 43,000
Note Purchase Agreement 2013 and 2016 [Member]
Debt Instrument [Line Items]
Debt Covenant, Minimum Consolidated Net Worth Calculation, Base Value					1,046,619
Foreign Performance Guarantee Facilities [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					10,058
Outstanding borrowings					0
Foreign Lines of Credit And Overdraft Facilities [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					7,530
Outstanding borrowings					0
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt financing costs				$ 2,359
Balance of unamortized debt issuance costs, line of credit			3,134		2,259
Line of Credit Facility, Maximum Borrowing Capacity					1,000,000
Outstanding borrowings			$ 156,700		$ 32,600
Credit facility effective interest rate on outstanding borrowing	2.29%		1.77%		2.29%
Third Amended and Restated Credit Agreement [Member]
Debt Instrument [Line Items]
Balance of unamortized debt issuance costs, line of credit						$ 2,014
Revolving Credit Agreement [Member]
Debt Instrument [Line Items]
Variable Rate Basis	LIBOR	LIBOR
Debt Covenant, Leverage Ratio, Maximum	3.5	3.5
Debt Covenant, Minimum Consolidated Net Worth Calculation, Base Value					$ 800,000
Debt Covenant, Minimum Consolidated Net Worth Calculation, Percentage of Net Income	50.00%				50.00%
Debt Covenant, Leverage Ratio During Material Acquisition Period, Maximum	4.0	4.0
Balance of unamortized debt issuance costs, line of credit					$ 2,259
Line of Credit Facility, Expiration Date	Apr. 01, 2020	Apr. 01, 2020
Line of Credit Facility, Maximum Borrowing Capacity					$ 1,000,000
Revolving Credit Agreement [Member] | Minimum [Member]
Debt Instrument [Line Items]
Basis Spread On Variable Rate	0.85%	0.85%
Revolving Credit Agreement [Member] | Maximum [Member]
Debt Instrument [Line Items]
Basis Spread On Variable Rate	1.65%	1.65%