Organization (Real Estate Investments) (Details) - real_estate_investment	27 Months Ended
	Mar. 31, 2018	Dec. 31, 2015
Real Estate Investments And Segment [Line Items]
Number of real estate investments	34	45
Number real estate investments sold	11
Domestic office investments
Real Estate Investments And Segment [Line Items]
Number of real estate investments	9
Domestic other investments
Real Estate Investments And Segment [Line Items]
Number of real estate investments	5
International office investments
Real Estate Investments And Segment [Line Items]
Number of real estate investments	9
International other investments
Real Estate Investments And Segment [Line Items]
Number of real estate investments	11