Borrowings (Westpac Bank Corporate Credit Facility (NZ)) (Narrative) (Details) $ in Thousands, $ in Millions					3 Months Ended					12 Months Ended
	May 07, 2021 USD ($)	May 07, 2021 NZD ($)	Dec. 20, 2018 NZD ($)	Dec. 19, 2018 NZD ($)	Mar. 31, 2021 USD ($)		Mar. 31, 2021 NZD ($)		Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)		Jul. 27, 2020
Debt Instrument [Line Items]
Contractual facility					$ 248,072					$ 300,449
Repayment of long-term borrowings					42,552				$ 22,733
Westpac Bank Corporate Credit Facility [Member]
Debt Instrument [Line Items]
Contractual facility					$ 22,365	[1]	$ 32.0			$ 23,021	[2]
Maturity date					Dec. 31, 2023	[1]	Dec. 31, 2023	[1]		Dec. 31, 2023	[2]
Interest rate			1.10%									1.65%
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
Subsequent Event [Member] | Westpac Bank Corporate Credit Facility [Member]
Debt Instrument [Line Items]
Repayment of long-term borrowings	$ 11,200	$ 16.0

[1] The contractual facilities and outstanding balances of the foreign currency denominated borrowings were translated into U.S. dollars based on the applicable exchange rates as of March 31, 2021.

[2] The contractual facilities and outstanding balances of the foreign currency denominated borrowings were translated into U.S. dollars based on the applicable exchange rates as of December 31, 2020.