SEGMENT INFORMATION - Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Revenues:
Rental income	$ 352,101	$ 357,340
Income from loans and investments	9,847	19,010
Interest and other income	536	341
Total revenues	1,017,554	910,291
Less:
Interest and other income	536	341
Property-level operating expenses	542,721	486,600
Office building and other services costs	1,313	618
Segment NOI	472,984	422,732
Interest and other income	536	341
Interest expense	(110,794)	(110,767)
Depreciation and amortization	(289,064)	(314,148)
General, administrative and professional fees	(42,998)	(40,309)
Loss on extinguishment of debt, net	0	(27,090)
Transaction expenses and deal costs	(19,992)	(4,617)
Allowance on loans receivable and investments	54	8,902
Other	27,190	9,428
Loss from unconsolidated entities	(4,269)	(250)
Gain on real estate dispositions	2,455	2,533
Income tax benefit (expense)	4,490	(2,153)
Income (loss) from continuing operations	40,592	(55,398)
Net income (loss)	40,592	(55,398)
Net income attributable to noncontrolling interests	1,860	1,811
Net income (loss) attributable to common stockholders	38,732	(57,209)
Resident fees and services
Revenues:
Other revenues	651,121	528,650
Office building and other services revenue
Revenues:
Other revenues	3,949	4,950
Operating Segments | Triple-Net Leased Properties
Revenues:
Rental income	151,561	159,885
Income from loans and investments	0	0
Interest and other income	0	0
Total revenues	151,561	159,885
Less:
Interest and other income	0	0
Property-level operating expenses	4,008	4,825
Office building and other services costs	0	0
Segment NOI	147,553	155,060
Interest and other income	0	0
Operating Segments | Triple-Net Leased Properties | Resident fees and services
Revenues:
Other revenues	0	0
Operating Segments | Triple-Net Leased Properties | Office building and other services revenue
Revenues:
Other revenues	0	0
Operating Segments | Senior Living Operations
Revenues:
Rental income	0	0
Income from loans and investments	0	0
Interest and other income	0	0
Total revenues	651,121	528,650
Less:
Interest and other income	0	0
Property-level operating expenses	475,530	417,829
Office building and other services costs	0	0
Segment NOI	175,591	110,821
Interest and other income	0	0
Operating Segments | Senior Living Operations | Resident fees and services
Revenues:
Other revenues	651,121	528,650
Operating Segments | Senior Living Operations | Office building and other services revenue
Revenues:
Other revenues	0	0
Operating Segments | Office Operations
Revenues:
Rental income	200,540	197,455
Income from loans and investments	0	0
Interest and other income	0	0
Total revenues	201,157	199,800
Less:
Interest and other income	0	0
Property-level operating expenses	63,183	63,946
Office building and other services costs	0	618
Segment NOI	137,974	135,236
Interest and other income	0	0
Operating Segments | Office Operations | Resident fees and services
Revenues:
Other revenues	0	0
Operating Segments | Office Operations | Office building and other services revenue
Revenues:
Other revenues	617	2,345
Non-Segment
Revenues:
Rental income	0	0
Income from loans and investments	9,847	19,010
Interest and other income	536	341
Total revenues	13,715	21,956
Less:
Interest and other income	536	341
Property-level operating expenses	0	0
Office building and other services costs	1,313	0
Segment NOI	11,866	21,615
Interest and other income	536	341
Non-Segment | Resident fees and services
Revenues:
Other revenues	0	0
Non-Segment | Office building and other services revenue
Revenues:
Other revenues	$ 3,332	$ 2,605