Investment in Unconsolidated Entities - Schedule Investment in Unconsolidated Entities (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Assets
Other assets	$ 25,696				$ 25,696		$ 22,836
Total assets	2,534,329				2,534,329		2,507,188
Liabilities and equity:
Other liabilities	39,279				39,279		29,039
Equity	1,759,532	$ 1,788,123	$ 1,810,697	$ 1,829,263	1,759,532	$ 1,810,697	1,819,601	$ 1,852,314
Total liabilities and stockholders' equity	2,534,329				2,534,329		2,507,188
Carrying value of investments in unconsolidated entities	116,824				116,824		118,861
Operating expenses
Total income	41,639		57,294		94,077	114,149
Depreciation and amortization	(22,405)		(24,692)		(44,527)	(47,554)
Real estate taxes	(7,218)		(8,958)		(15,707)	(18,009)
Interest expense, net	(4,924)		(5,627)		(9,733)	(11,105)
General and administrative	(8,387)		(8,886)		(15,582)	(17,409)
Loss on extinguishment of debt	(2,543)		(809)		(2,543)	(809)
Provision for asset impairment	0		0		(9,002)	0
Net loss	(9,611)	$ (3,486)	(5,722)	$ (9,499)	(13,097)	(15,221)
Equity in (losses) earnings of unconsolidated entities	(149)		(1,079)		640	(620)
IAGM Retail Fund I, LLC
Liabilities and equity:
Accumulated amortization	11				11
Equity Method Investment, Nonconsolidated Investee or Group of Investees
Operating expenses
Net loss	(285)		(1,974)		2,970	(6,074)
Company's share of net (loss) income	(157)		(1,079)		1,587	(5,023)
Equity in (losses) earnings of unconsolidated entities	(149)		(1,079)		640	(620)
Equity Method Investment, Nonconsolidated Investee or Group of Investees | IAGM Retail Fund I, LLC
Assets
Real estate assets, net of accumulated depreciation	402,799				402,799		425,585
Other assets	67,342				67,342		66,437
Total assets	470,141				470,141		492,022
Liabilities and equity:
Mortgages payable, net	242,115				242,115		256,732
Other liabilities	15,458				15,458		20,765
Equity	212,568				212,568		214,525
Total liabilities and stockholders' equity	470,141				470,141		492,022
Company's share of equity	117,771				117,771		118,861
Deferred gain, net of accumulated amortization of $11	(947)				(947)		0
Carrying value of investments in unconsolidated entities	116,824				116,824		$ 118,861
Operating expenses
Total income	9,815		13,113		22,538	26,753
Depreciation and amortization	(4,316)		(5,663)		(8,658)	(10,939)
Property operating	(1,702)		(2,047)		(3,823)	(4,023)
Real estate taxes	(2,182)		(2,355)		(4,608)	(4,961)
Interest expense, net	(1,775)		(2,894)		(3,968)	(5,788)
General and administrative	(125)		(126)		(244)	(245)
(Loss) gain on sale of real estate, net	0		(559)		1,741	(559)
Loss on extinguishment of debt	0		0		(8)	0
Provision for asset impairment	0		(1,443)		0	(1,443)
Net loss	(285)		(1,974)		2,970	(1,205)
Outside basis adjustment for investee's sale of real estate	8		0		(947)	0
Equity Method Investment, Nonconsolidated Investee or Group of Investees | Downtown Railyard Venture, LLC
Operating expenses
Net loss	0		0		0	(4,869)
Outside basis adjustment for investee's sale of real estate	$ 0		$ 0		$ 0	$ 4,403