Segment Reporting - Segment Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Rental and resident fee income						$ 145,404
Net interest income on debt and securities						5,145
Other revenue	$ 1,003		$ 930		$ 1,360	1,678
Property operating expenses	(44,636)		(47,731)		(89,854)	(94,157)
Interest expense	(17,294)		(17,693)		(34,690)	(34,731)
Other expenses related to securitization trust	0		0		0	(811)
Transaction costs	(38)		(41)		(76)	(804)
Asset management and other fees - related party	(4,995)		(5,951)		(9,989)	(11,894)
General and administrative expenses	(2,349)		(3,424)		(5,403)	(7,111)
Depreciation and amortization	(15,962)		(27,494)		(38,361)	(56,314)
Impairment of operating real estate	(10,146)		(2,456)		(10,146)	(5,239)
Unrealized gain (loss) on senior housing mortgage loans and debt held in securitization trust, net						0
Realized gain (loss) on investments and other	5,485		0		5,722	3,495
Income (loss) before equity in earnings (losses) of unconsolidated ventures and income tax benefit (expense)	(13,040)		(30,092)		(31,479)	(55,339)
Equity in earnings (losses) of unconsolidated ventures	(4,405)		(4,098)		(4,629)	(12,724)
Income tax benefit (expense)	(15)		(15)		(21)	(30)
Net income (loss)	(17,460)	$ (18,669)	(34,205)	$ (33,888)	(36,129)	(68,093)
Discount accretion income					55	49
Operating Segments
Segment Reporting Information [Line Items]
Rental and resident fee income	73,969		71,847		146,133	145,404
Net interest income on debt and securities	1,923		1,921		3,825	4,334
Other revenue	1,003		930		1,360	1,678
Property operating expenses	(44,636)		(47,731)		(89,854)	(94,157)
Interest expense	(17,294)		(17,693)		(34,690)	(34,731)
Other expenses related to securitization trust						0
Transaction costs	(38)		(41)		(76)	(804)
Asset management and other fees - related party	(4,995)		(5,951)		(9,989)	(11,894)
General and administrative expenses	(2,349)		(3,424)		(5,403)	(7,111)
Depreciation and amortization	(15,962)		(27,494)		(38,361)	(56,314)
Impairment of operating real estate	(10,146)		(2,456)		(10,146)	(5,239)
Unrealized gain (loss) on senior housing mortgage loans and debt held in securitization trust, net						0
Realized gain (loss) on investments and other	5,485				5,722	3,495
Income (loss) before equity in earnings (losses) of unconsolidated ventures and income tax benefit (expense)	(13,040)		(30,092)		(31,479)	(55,339)
Equity in earnings (losses) of unconsolidated ventures	(4,405)		(4,098)		(4,629)	(12,724)
Income tax benefit (expense)	(15)		(15)		(21)	(30)
Net income (loss)	(17,460)		(34,205)		(36,129)	(68,093)
Operating Segments | Net Lease
Segment Reporting Information [Line Items]
Rental and resident fee income	8,446		7,950		16,998	16,696
Net interest income on debt and securities	0		0		0	0
Other revenue	0		0		1	0
Property operating expenses	(1)		(825)		(1)	(834)
Interest expense	(3,124)		(3,306)		(6,399)	(6,707)
Other expenses related to securitization trust						0
Transaction costs	0		0		0	0
Asset management and other fees - related party	0		0		0	0
General and administrative expenses	(97)		(56)		(112)	(61)
Depreciation and amortization	(3,499)		(3,368)		(7,063)	(6,720)
Impairment of operating real estate	(146)		(2,456)		(146)	(2,456)
Unrealized gain (loss) on senior housing mortgage loans and debt held in securitization trust, net						0
Realized gain (loss) on investments and other	5,871				5,871	0
Income (loss) before equity in earnings (losses) of unconsolidated ventures and income tax benefit (expense)	7,450		(2,061)		9,149	(82)
Equity in earnings (losses) of unconsolidated ventures	0		0		0	0
Income tax benefit (expense)	0		0		0	0
Net income (loss)	7,450		(2,061)		9,149	(82)
Operating Segments | Operating
Segment Reporting Information [Line Items]
Rental and resident fee income	65,523		63,897		129,135	128,708
Net interest income on debt and securities	0		0		0	0
Other revenue	760		728		760	1,383
Property operating expenses	(44,635)		(46,906)		(89,853)	(93,323)
Interest expense	(14,148)		(14,304)		(28,189)	(27,913)
Other expenses related to securitization trust						0
Transaction costs	(38)		0		(76)	(763)
Asset management and other fees - related party	0		0		0	0
General and administrative expenses	(25)		(128)		(37)	(441)
Depreciation and amortization	(12,463)		(24,126)		(31,298)	(49,594)
Impairment of operating real estate	(10,000)		0		(10,000)	(2,783)
Unrealized gain (loss) on senior housing mortgage loans and debt held in securitization trust, net						0
Realized gain (loss) on investments and other	(10)				227	0
Income (loss) before equity in earnings (losses) of unconsolidated ventures and income tax benefit (expense)	(15,036)		(20,839)		(29,331)	(44,726)
Equity in earnings (losses) of unconsolidated ventures	0		0		0	0
Income tax benefit (expense)	(15)		(15)		(21)	(30)
Net income (loss)	(15,051)		(20,854)		(29,352)	(44,756)
Operating Segments | Unconsolidated Investments
Segment Reporting Information [Line Items]
Rental and resident fee income	0		0		0	0
Net interest income on debt and securities	0		0		0	0
Other revenue	0		0		0	0
Property operating expenses	0		0		0	0
Interest expense	0		0		0	0
Other expenses related to securitization trust						0
Transaction costs	0		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 of operating real estate	0		0		0	0
Unrealized gain (loss) on senior housing mortgage loans and debt held in securitization trust, net						0
Realized gain (loss) on investments and other	0				0	0
Income (loss) before equity in earnings (losses) of unconsolidated ventures and income tax benefit (expense)	0		0		0	0
Equity in earnings (losses) of unconsolidated ventures	(4,405)		(4,098)		(4,629)	(12,724)
Income tax benefit (expense)	0		0		0	0
Net income (loss)	(4,405)		(4,098)		(4,629)	(12,724)
Operating Segments | Debt and Securities
Segment Reporting Information [Line Items]
Rental and resident fee income	0		0		0	0
Net interest income on debt and securities	1,923		1,921		3,825	4,648
Other revenue	10		0		19	0
Property operating expenses	0		0		0	0
Interest expense	0		0		0	0
Other expenses related to securitization trust						0
Transaction costs	0		0		0	0
Asset management and other fees - related party	0		0		0	0
General and administrative expenses	(9)		(10)		(19)	(25)
Depreciation and amortization	0		0		0	0
Impairment of operating real estate	0		0		0	0
Unrealized gain (loss) on senior housing mortgage loans and debt held in securitization trust, net						(314)
Realized gain (loss) on investments and other	0				0	3,495
Income (loss) before equity in earnings (losses) of unconsolidated ventures and income tax benefit (expense)	1,924		1,911		3,825	7,804
Equity in earnings (losses) of unconsolidated ventures	0		0		0	0
Income tax benefit (expense)	0		0		0	0
Net income (loss)	1,924		1,911		3,825	7,804
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Rental and resident fee income	0		0		0	0
Net interest income on debt and securities	0		0		0	(314)
Other revenue	233		202		580	295
Property operating expenses	0		0		0	0
Interest expense	(22)		(83)		(102)	(111)
Other expenses related to securitization trust						0
Transaction costs	0		(41)		0	(41)
Asset management and other fees - related party	(4,995)		(5,951)		(9,989)	(11,894)
General and administrative expenses	(2,218)		(3,230)		(5,235)	(6,584)
Depreciation and amortization	0		0		0	0
Impairment of operating real estate	0		0		0	0
Unrealized gain (loss) on senior housing mortgage loans and debt held in securitization trust, net						314
Realized gain (loss) on investments and other	(376)				(376)	0
Income (loss) before equity in earnings (losses) of unconsolidated ventures and income tax benefit (expense)	(7,378)		(9,103)		(15,122)	(18,335)
Equity in earnings (losses) of unconsolidated ventures	0		0		0	0
Income tax benefit (expense)	0		0		0	0
Net income (loss)	$ (7,378)		$ (9,103)		$ (15,122)	(18,335)
Discount accretion income						300
Segment Reconciling Items
Segment Reporting Information [Line Items]
Rental and resident fee income						0
Net interest income on debt and securities						811
Other revenue						0
Property operating expenses						0
Interest expense						0
Other expenses related to securitization trust						(811)
Transaction costs						0
Asset management and other fees - related party						0
General and administrative expenses						0
Depreciation and amortization						0
Impairment of operating real estate						0
Unrealized gain (loss) on senior housing mortgage loans and debt held in securitization trust, net						0
Realized gain (loss) on investments and other						0
Income (loss) before equity in earnings (losses) of unconsolidated ventures and income tax benefit (expense)						0
Equity in earnings (losses) of unconsolidated ventures						0
Income tax benefit (expense)						0
Net income (loss)						$ 0