Debt (Westpac Bank Corporate Credit Facility (NZ)) (Narrative) (Details) $ in Thousands, $ in Millions			9 Months Ended		12 Months Ended
	Dec. 20, 2018 NZD ($)	Dec. 19, 2018 NZD ($)	Sep. 30, 2020 USD ($)		Dec. 31, 2019 USD ($)		Jul. 27, 2020	Jul. 01, 2020 USD ($)	Jul. 01, 2020 NZD ($)
Debt Instrument [Line Items]
Contractual facility			$ 289,876		$ 283,138
Westpac Bank Corporate Credit Facility [Member]
Debt Instrument [Line Items]
Contractual facility			$ 21,146	[1]	$ 21,584	[2]
Maturity date			Dec. 31, 2023	[1]	Dec. 31, 2023	[2]
Interest rate	1.10%						1.65%
Cash transferred to a term deposit								$ 10,600	$ 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

[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 September 30, 2020.

[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, 2019.