Segment Reporting - Segment Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Property and other revenues	$ 67,755			$ 72,778			$ 209,954	$ 220,271
Interest income on debt investments	1,927			1,946			5,738	5,771
Real estate properties - operating expenses	(46,501)			(45,359)			(137,530)	(135,213)
Interest expense	(16,459)			(17,218)			(49,591)	(51,908)
Transaction costs	0			(29)			(7)	(105)
Asset management and other fees - related party	(4,431)			(4,994)			(13,293)	(14,983)
General and administrative expenses	(3,446)			(2,807)			(8,763)	(8,210)
Depreciation and amortization	(15,945)			(16,164)			(48,929)	(54,525)
Impairment loss	0			0			(91,437)	(10,146)
Realized gain (loss) on investments and other	0			204			0	5,926
Equity in earnings (losses) of unconsolidated ventures	(1,043)			(3,037)			(36,799)	(7,666)
Income tax expense	(15)			(17)			(43)	(38)
Net income (loss)	(18,158)	$ (139,995)	$ (12,547)	(14,697)	$ (17,460)	$ (18,669)	(170,700)	(50,826)
Net Lease
Segment Reporting Information [Line Items]
Property and other revenues	8,225			8,204			24,673	25,203
Interest income on debt investments	0			0			0	0
Real estate properties - operating expenses	0			(5)			(13)	(5)
Interest expense	(2,967)			(3,025)			(8,879)	(9,424)
Transaction costs				0			0	0
Asset management and other fees - related party	0			0			0	0
General and administrative expenses	(562)			(47)			(667)	(159)
Depreciation and amortization	(3,722)			(3,595)			(11,123)	(10,657)
Impairment loss							(722)	(146)
Realized gain (loss) on investments and other				0				5,871
Equity in earnings (losses) of unconsolidated ventures	0			0			0	0
Income tax expense	0			0			0	0
Net income (loss)	974			1,532			3,269	10,683
Operating
Segment Reporting Information [Line Items]
Property and other revenues	59,507			64,496			185,118	194,391
Interest income on debt investments	0			0			0	0
Real estate properties - operating expenses	(46,501)			(45,354)			(137,517)	(135,208)
Interest expense	(13,165)			(14,193)			(40,089)	(42,382)
Transaction costs				(29)			(7)	(105)
Asset management and other fees - related party	0			0			0	0
General and administrative expenses	(82)			19			(182)	(17)
Depreciation and amortization	(12,223)			(12,569)			(37,806)	(43,868)
Impairment loss							(90,715)	(10,000)
Realized gain (loss) on investments and other				204				431
Equity in earnings (losses) of unconsolidated ventures	0			0			0	0
Income tax expense	(15)			(17)			(43)	(38)
Net income (loss)	(12,479)			(7,443)			(121,241)	(36,796)
Unconsolidated Investments
Segment Reporting Information [Line Items]
Property and other revenues	0			0			0	0
Interest income on debt investments	0			0			0	0
Real estate properties - operating expenses	0			0			0	0
Interest expense	0			0			0	0
Transaction costs				0			0	0
Asset management and other fees - related party	0			0			0	0
General and administrative expenses	0			0			0	0
Depreciation and amortization	0			0			0	0
Impairment loss							0	0
Realized gain (loss) on investments and other				0				0
Equity in earnings (losses) of unconsolidated ventures	(1,043)			(3,037)			(36,799)	(7,666)
Income tax expense	0			0			0	0
Net income (loss)	(1,043)			(3,037)			(36,799)	(7,666)
Debt and Securities
Segment Reporting Information [Line Items]
Property and other revenues	0			10			0	29
Interest income on debt investments	1,927			1,946			5,738	5,771
Real estate properties - operating expenses	0			0			0	0
Interest expense	0			0			0	0
Transaction costs				0			0	0
Asset management and other fees - related party	0			0			0	0
General and administrative expenses	0			(10)			(19)	(28)
Depreciation and amortization	0			0			0	0
Impairment loss							0	0
Realized gain (loss) on investments and other				0				0
Equity in earnings (losses) of unconsolidated ventures	0			0			0	0
Income tax expense	0			0			0	0
Net income (loss)	1,927			1,946			5,719	5,772
Corporate
Segment Reporting Information [Line Items]
Property and other revenues	23			68			163	648
Interest income on debt investments	0			0			0	0
Real estate properties - operating expenses	0			0			0	0
Interest expense	(327)			0			(623)	(102)
Transaction costs				0			0	0
Asset management and other fees - related party	(4,431)			(4,994)			(13,293)	(14,983)
General and administrative expenses	(2,802)			(2,769)			(7,895)	(8,006)
Depreciation and amortization	0			0			0	0
Impairment loss							0	0
Realized gain (loss) on investments and other				0				(376)
Equity in earnings (losses) of unconsolidated ventures	0			0			0	0
Income tax expense	0			0			0	0
Net income (loss)	$ (7,537)			$ (7,695)			$ (21,648)	$ (22,819)