Real Estate (Real Estate Available and Held for Sale) (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) lease_asset	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Real Estate Properties [Line Items]
Property transferred to held for sale, aggregate, carrying value	$ 21,000	$ 17,900	$ 11,100
Commercial Operating Properties
Real Estate Properties [Line Items]
Property transferred from held for sale, aggregate, carrying value			2,900,000
Operating Properties
Real Estate Properties [Line Items]
Property transferred to held for sale, aggregate, carrying value	20,100	16,100	2,900
Net Lease
Real Estate Properties [Line Items]
Property transferred to held for sale, aggregate, carrying value	$ 900	$ 1,800	$ 8,200
Condominium Units
Real Estate Properties [Line Items]
Number of residential units \| lease_asset	2
Property transferred from held for sale, aggregate, carrying value	$ 1,800,000