Intangible Assets and Liabilities - Summary of Intangible Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Assets
Gross	$ 656,852	$ 665,679
Accumulated amortization	(418,996)	(387,827)
Total	$ 237,856	$ 277,852
Weighted Average Remaining Amortization in Years	9 years 4 months 24 days	9 years 4 months 24 days
Liabilities
Accumulated amortization	$ (28,074)	$ (27,187)
Total	$ 33,586	$ 38,779
Weighted Average Remaining Amortization in Years	14 years 6 months	13 years 10 months 24 days
Below market leases
Liabilities
Gross	$ 61,660	$ 65,966
Weighted Average Remaining Amortization in Years	14 years 6 months	13 years 10 months 24 days
In place leases
Assets
Gross	$ 473,776	$ 481,173
Weighted Average Remaining Amortization in Years	9 years 7 months 6 days	9 years 6 months
Tenant relationships
Assets
Gross	$ 145,272	$ 146,893
Weighted Average Remaining Amortization in Years	9 years 10 months 24 days	9 years 8 months 12 days
Above market leases
Assets
Gross	$ 37,804	$ 37,613
Weighted Average Remaining Amortization in Years	5 years 10 months 24 days	6 years 2 months 12 days