Derivative Instruments and Hedging Activities (Narrative) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021 USD ($) Swap loan	Mar. 31, 2020 USD ($)	Mar. 31, 2021 USD ($) Swap loan	Mar. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	May 31, 2018 USD ($) loan	Sep. 23, 2016 EUR (€)
Derivative Instruments Gain Loss [Line Items]
Derivative, notional amount	$ 33,750		$ 33,750
Remaining unrecognzied gains (losses) associated with derivative instruments included in AOCI	(42,620)		$ (42,620)		$ (21,132)
2016 Note Purchase Agreements [Member]
Derivative Instruments Gain Loss [Line Items]
Issuance date			Sep. 23, 2016
Face amount | €							€ 160,000,000
Series M Notes [Member]
Derivative Instruments Gain Loss [Line Items]
Face amount | €							€ 40,000,000
Maturity date			Sep. 23, 2026
Gain (Loss) on foreign currency transaction designated as a hedge of a net investment in a foreign subsidiary	2,329	$ 650	$ 102	$ (395)
Floating-Rate Cross Currency Interest Rate Contract [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative, notional amount						$ 167,420
2020 Fixed-Rate Cross-Currency Swaps [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative, notional amount	$ 400,000		$ 400,000
2020 Fixed-Rate Cross-Currency Swaps [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative, notional amount						400,000
Derivative, number of instruments | Swap	5		5
2020 Floating-Rate Cross-Currency Swap [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative, notional amount	$ 45,000		$ 45,000
Fixed-Rate Cross Currency Interest Rate Contract [Member] | Designated as Hedging Instrument | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative, notional amount						$ 400,000
Derivative, number of instruments | loan	5		5			5