Intangible Assets and Liabilities - Intangible Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Intangible Assets [Line Items]
Intangible assets, total cost	$ 93,254	$ 177,581
Intangible assets, accumulated amortization	(42,539)	(92,730)
Intangible assets, net	50,715	84,851
Intangible liabilities, net		44,757
Acquired lease intangibles, accumulated amortization		(22,494)
Acquired lease intangibles, net	17,500	22,263
In-place lease value
Intangible Assets [Line Items]
Intangible assets, total cost	89,504	167,357
Intangible assets, accumulated amortization	(39,302)	(84,123)
Intangible assets, net	50,202	83,234
Tenant relationship value
Intangible Assets [Line Items]
Intangible assets, total cost	2,610	5,268
Intangible assets, accumulated amortization	(2,399)	(4,815)
Intangible assets, net	211	453
Above market leases acquired
Intangible Assets [Line Items]
Intangible assets, total cost	1,140	4,956
Intangible assets, accumulated amortization	(838)	(3,792)
Intangible assets, net	302	$ 1,164
Below market leases acquired
Intangible Assets [Line Items]
Intangible liabilities, net	29,189
Acquired lease intangibles, accumulated amortization	(11,689)
Acquired lease intangibles, net	$ 17,500