Derivative Financial Instruments Outstanding Interest Rate Swap Agreements (Details) $ in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019 AUD ($)	Mar. 31, 2019 USD ($)
Australia Dollar Interest Rate Swap [Member]
Derivative [Line Items]
Effective Date	Dec. 01, 2016
Settlement Date	Dec. 01, 2021
Notional Amount	$ 517,500
Pay Fixed Rate	2.44%	2.44%
United States Dollar Interest Rate Swaps [Member]
Derivative [Line Items]
Effective Date	Aug. 31, 2018
Notional Amount		$ 500,000
United States Dollar Interest Rate Swaps [Member] | Minimum [Member]
Derivative [Line Items]
Settlement Date	Aug. 31, 2021
Pay Fixed Rate	2.70%	2.70%
United States Dollar Interest Rate Swaps [Member] | Maximum [Member]
Derivative [Line Items]
Settlement Date	Aug. 31, 2048
Pay Fixed Rate	2.87%	2.87%