Leases - Operating Leases (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($) shopping_center	Jun. 30, 2016 USD ($)
Operating Leased Assets [Line Items]
Number of shopping centers with land leases | shopping_center	7
Ground lease expense	$ 1.8	$ 1.0
Rent expense capitalized	0.1	0.3
Rent expense	$ 0.4	$ 0.2
Minimum
Operating Leased Assets [Line Items]
Period of lease term	25 years
Maximum
Operating Leased Assets [Line Items]
Period of lease term	71 years