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Derivative Financial Instruments and Fair Value Measurements - Cash Flow Hedges (Details) - Designated as Hedging Instrument - Cash Flow Hedging $ in Millions, $ in Millions	Mar. 31, 2018 AUD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2017 AUD ($)	Sep. 30, 2017 USD ($)
Interest Rate Swap June 2018 | USD
Derivative financial instruments
Notional Amount		$ 300.0		$ 300.0
Fixed Rate (as a percent)	1.63%	1.63%	1.63%	1.63%
Interest Rate Swap September 2018 | USD
Derivative financial instruments
Notional Amount		$ 300.0		$ 300.0
Fixed Rate (as a percent)	1.54%	1.54%	1.54%	1.54%
Interest Rate Swap February 2021 | AUD
Derivative financial instruments
Notional Amount		$ 200.0
Fixed Rate (as a percent)	2.19%	2.19%
Interest Rate Swap September 2022 | CAD
Derivative financial instruments
Notional Amount		$ 400.0
Fixed Rate (as a percent)	2.49%	2.49%
Interest Rate Swap February 2023 | USD
Derivative financial instruments
Notional Amount		$ 200.0
Fixed Rate (as a percent)	2.60%	2.60%
Foreign currency contracts
Derivative financial instruments
Notional principal of derivative exchange contracts	$ 2.9	$ 2.3	$ 15.1	$ 11.3

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- Definition

Aggregate notional amount of foreign currency derivatives to exchange foreign currencies. Notional amount refers to the number of currency units specified in the foreign currency derivative contract.

+ References

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Fixed interest rate related to the interest rate derivative.

+ References

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