Borrowings (Westpac Bank Corporate Credit Facility (NZ)) (Narrative) (Details) $ in Thousands, $ in Millions					9 Months Ended		12 Months Ended
	Aug. 30, 2021 NZD ($)	May 07, 2021 NZD ($)	Dec. 20, 2018 NZD ($)	Dec. 19, 2018 NZD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Jul. 27, 2020
Debt Instrument [Line Items]
Contractual facility					$ 269,953		$ 300,449
Repayment of long-term borrowings					79,357	$ 28,910
Westpac Bank Corporate Credit Facility [Member]
Debt Instrument [Line Items]
Contractual facility	$ 13.8	$ 16.0			$ 9,548		$ 23,021
Maturity date					Dec. 31, 2023		Dec. 31, 2023
Interest rate			1.10%					1.65%
Repayment of long-term borrowings	$ 2.2	$ 16.0
Westpac Bank Corporate Credit Facility [Member] | Bank Bill Swap Bid Rate [Member]
Debt Instrument [Line Items]
Interest rate								2.40%
Westpac Bank Corporate Credit Facility, Tranche 1 [Member]
Debt Instrument [Line Items]
Contractual facility			$ 32.0	$ 35.0
Westpac Bank Corporate Credit Facility, Tranche 1 [Member] | Bank Bill Swap Bid Rate [Member]
Debt Instrument [Line Items]
Interest rate			1.75%
Westpac Bank Corporate Credit Facility, Tranche 2 [Member]
Debt Instrument [Line Items]
Contractual facility			$ 18.0