Operating Leases (Details)	12 Months Ended
	Dec. 31, 2017 State Property mo
Operating Leased Assets [Line Items]
Number of states where retail, office and mixed-use properties are located | State	5
Number of office, retail, and multifamily operating leases	26
Years, minimum term range of office and retail leases	3 years
Years, maximum term range of office and retail leases	10 years
Months, minimum term of apartment leases	7 months
Months, maximum term of apartment leases	15 months
Future minimum rentals term, maximum | mo	12
Retail Or Office
Operating Leased Assets [Line Items]
Number of office, retail, and multifamily operating leases	813
Residential Property
Operating Leased Assets [Line Items]
Number of office, retail, and multifamily operating leases	1,844