Segment Information (Income Statement by Segment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues
Rental income	$ 1,448,120	$ 1,494,892	$ 1,609,876
Interest and other income	14,809	7,609	10,984
Total revenues	3,828,007	3,795,357	3,872,750
Less:
Interest and other income	14,809	7,609	10,984
Property-level operating expenses	2,084,064	1,937,443	1,808,208
Office building and other services costs	4,433	2,315	2,319
Segment NOI	1,724,701	1,847,990	2,051,239
Interest expense	(440,089)	(469,541)	(451,662)
Depreciation and amortization	(1,197,403)	(1,109,763)	(1,045,620)
General, administrative and professional fees	(129,758)	(130,158)	(158,726)
Loss on extinguishment of debt, net	(59,299)	(10,791)	(41,900)
Transaction expenses and deal costs	(47,318)	(29,812)	(15,235)
Allowance on loans receivable and investments	9,082	(24,238)
Other	37,110	707	(10,339)
Income (loss) from unconsolidated entities	4,983	1,844	(2,454)
Gain on real estate dispositions	218,788	262,218	26,022
Income tax (expense) benefit	(4,827)	96,534	56,310
Income from continuing operations	56,559	441,185	439,297
Net income	56,559	441,185	439,297
Other comprehensive (loss) income	7,551	2,036	6,281
Net income	49,008	439,149	433,016
Income from loans and investments	74,981	80,505	89,201
Other	37,110	707	(10,339)
Income from loans and investments	74,981	80,505	89,201
Operating Segments | Triple-net leased properties
Revenues
Rental income	653,823	695,265	780,898
Interest and other income	0	0	0
Total revenues	653,823	695,265	780,898
Less:
Interest and other income	0	0	0
Property-level operating expenses	15,335	22,160	26,561
Office building and other services costs	0	0	0
Segment NOI	638,488	673,105	754,337
Income from loans and investments	0	0	0
Income from loans and investments	0	0	0
Operating Segments | Senior living operations
Revenues
Rental income	0	0	0
Interest and other income	0	0	0
Total revenues	2,270,001	2,197,160	2,151,533
Less:
Interest and other income	0	0	0
Property-level operating expenses	1,811,728	1,658,671	1,521,398
Office building and other services costs	0	0	0
Segment NOI	458,273	538,489	630,135
Income from loans and investments	0	0	0
Income from loans and investments	0	0	0
Operating Segments | Office operations
Revenues
Rental income	794,297	799,627	828,978
Interest and other income	0	0	0
Total revenues	802,681	808,302	836,725
Less:
Interest and other income	0	0	0
Property-level operating expenses	257,001	256,612	260,249
Office building and other services costs	1,798	2,315	2,319
Segment NOI	543,882	549,375	574,157
Income from loans and investments	0	0	0
Income from loans and investments	0	0	0
All Other
Revenues
Rental income	0	0	0
Interest and other income	14,809	7,609	10,984
Total revenues	101,502	94,630	103,594
Less:
Interest and other income	14,809	7,609	10,984
Property-level operating expenses	0	0	0
Office building and other services costs	2,635	0	0
Segment NOI	84,058	87,021	92,610
Income from loans and investments	74,981	80,505	89,201
Income from loans and investments	74,981	80,505	89,201
Resident fees and services
Revenues
Revenue from contracts with customers	2,270,001	2,197,160	2,151,533
Resident fees and services | Operating Segments | Triple-net leased properties
Revenues
Revenue from contracts with customers	0	0	0
Resident fees and services | Operating Segments | Senior living operations
Revenues
Revenue from contracts with customers	2,270,001	2,197,160	2,151,533
Resident fees and services | Operating Segments | Office operations
Revenues
Revenue from contracts with customers	0	0	0
Resident fees and services | All Other
Revenues
Revenue from contracts with customers	0	0	0
Office building and other services revenue
Revenues
Revenue from contracts with customers	20,096	15,191	11,156
Office building and other services revenue | Operating Segments | Triple-net leased properties
Revenues
Revenue from contracts with customers	0	0	0
Office building and other services revenue | Operating Segments | Senior living operations
Revenues
Revenue from contracts with customers	0	0	0
Office building and other services revenue | Operating Segments | Office operations
Revenues
Revenue from contracts with customers	8,384	8,675	7,747
Office building and other services revenue | All Other
Revenues
Revenue from contracts with customers	$ 11,712	$ 6,516	$ 3,409