Insurance Recoveries on Impairment and Related Losses Due to Earthquake (Narrative) (Details) $ in Thousands, $ in Thousands	1 Months Ended				12 Months Ended
	May 31, 2017 NZD ($)	May 31, 2017 USD ($)	Apr. 30, 2017 NZD ($)	Apr. 30, 2017 USD ($)	Dec. 31, 2017 NZD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 NZD ($)	Dec. 31, 2016 USD ($)
Insurance Recoveries on Impairment and Related Losses Due to Earthquake [Abstract]
Insurance coverage limit			$ 36,000	$ 25,000
Proceeds from insurance settlement	$ 28,900	$ 20,000					$ 7,100	$ 5,000
Total insurance gains					$ 14,849	$ 10,740