Investment Property (Intangible Assets Amortization) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
In-Place Leases
Finite Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	$ 18,300	$ 20,500
In-Place Leases
April 1, 2018 through December 31, 2018	35,962
2019	41,196
2020	34,420
2021	23,552
2022	18,596
Out-of-Market Leases, Net
Finite Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	(2,200)	$ 400
Out-of-Market Leases, Net
April 1, 2018 through December 31, 2018	(1,529)
2019	(3,141)
2020	(3,231)
2021	(851)
2022	$ (1,577)