Real Estate Intangibles - Summary of Real Estate Intangibles Excluding Those Classified as Held For Sale (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Assets:
Gross historical cost	$ 1,565,978	$ 1,617,051
Accumulated amortization	(1,178,515)	(1,181,158)
Net book value	$ 387,463	$ 435,893
Weighted-average amortization period in years	10 years 9 months 18 days	10 years 3 months 18 days
Liabilities:
Below market tenant leases	$ 83,037	$ 99,035
Accumulated amortization	(40,886)	(49,390)
Net book value	$ 42,151	$ 49,645
Weighted-average amortization period in years	8 years 4 months 24 days	8 years 7 months 6 days
In place lease intangibles
Assets:
Gross historical cost	$ 1,460,748	$ 1,513,836
Above market tenant leases
Assets:
Gross historical cost	58,780	59,540
Lease commissions
Assets:
Gross historical cost	$ 46,450	$ 43,675