Derivative Instruments and Hedging Activities (Narrative) (Details) € in Thousands, ¥ in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2018 EUR (€)	Sep. 30, 2017 CNY (¥)	Sep. 30, 2017 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Accumulated OCI on Derivative	$ 0	$ 0	$ 0	$ 0
Net unrecognized gains on terminated derivative instruments expected to be reclassified to earnings	$ 72
Term of gain or loss recognition in interest expense on terminated derivatives recorded in OCI	12 months
Face Amount | €					€ 160,000
EUR Denominated Loan [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on foreign currency transaction designated as a hedge of a net investment in a foreign subsidiary	$ (1,268)	(664)	(2,011)	$ 2,150
Intercompany Loan [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on foreign currency transaction designated as a hedge of a net investment in a foreign subsidiary		$ 281	735
Value of Net Investment Hedging Instruments Used | ¥						¥ 160,000
Total Accumulated Other Comprehensive (Loss) Earnings [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrecognized gains (loss)	$ 182		$ 182				$ 218
Series D Notes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Issuance Date			Oct. 01, 2008
Series F Notes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Issuance Date			Apr. 01, 2009
2013 Note Purchase Agreement [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Issuance Date	Oct. 01, 2013
Face Amount	$ 250,000		$ 250,000
First Closing Notes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Issuance Date			Oct. 01, 2013
Second Closing Notes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Issuance Date			Nov. 15, 2013
2016 Note Purchase Agreements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Issuance Date	Sep. 23, 2016		Sep. 23, 2016
Face Amount | €					160,000
Series M Notes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Face Amount | €					40,000
Series N Notes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Face Amount | €					77,000
Series O Notes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Face Amount | €					€ 43,000