Schedule III - Real Estate and Accumulated Depreciation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) property Property	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Summary of real estate properties
NUMBER OF PROP. | property	204
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
Gross real estate asset, Total	$ 4,359,993	$ 3,993,427	$ 3,907,010	$ 3,633,993
Accumulated depreciation	$ 1,121,102	$ 1,025,831	$ 933,220	$ 843,816
Medical Office [Member] | Minimum [Member]
Real Estate and Accumulated Depreciation [Line Items]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Date Acquired	Jan. 01, 1993
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Date of Construction	Jan. 01, 1906
Medical Office [Member] | Maximum [Member]
Real Estate and Accumulated Depreciation [Line Items]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Date Acquired	Dec. 31, 2017
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Date of Construction	Dec. 31, 2015
Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	204
LAND 1
INITIAL INVESTMENT	$ 274,121
COST CAPITALIZED subsequent to acquisition	10,408
TOTAL	284,529
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	3,361,046
COST CAPITALIZED subsequent to acquisition	621,470
TOTAL	3,982,516
PERSONAL PROPERTY	5,038
Gross real estate asset, Total	4,272,083
Accumulated depreciation	1,115,695
Encumbrances	$ 129,343
Construction in Progress [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	0
LAND 1
INITIAL INVESTMENT	$ 0
COST CAPITALIZED subsequent to acquisition	0
TOTAL	0
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	0
COST CAPITALIZED subsequent to acquisition	0
TOTAL	48,731
PERSONAL PROPERTY	0
Gross real estate asset, Total	48,731
Accumulated depreciation
Encumbrances	$ 0
Land Held for Development [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	0
LAND 1
INITIAL INVESTMENT	$ 24,647
COST CAPITALIZED subsequent to acquisition	0
TOTAL	24,647
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	0
COST CAPITALIZED subsequent to acquisition	0
TOTAL	0
PERSONAL PROPERTY	0
Gross real estate asset, Total	24,647
Accumulated depreciation	671
Encumbrances	$ 0
Memphis Redevelopment [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	0
LAND 1
INITIAL INVESTMENT	$ 5,222
COST CAPITALIZED subsequent to acquisition	0
TOTAL	5,222
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	3,810
COST CAPITALIZED subsequent to acquisition	0
TOTAL	3,810
PERSONAL PROPERTY	0
Gross real estate asset, Total	9,032
Accumulated depreciation	50
Encumbrances	$ 0
Corporate Property [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	0
LAND 1
INITIAL INVESTMENT	$ 0
COST CAPITALIZED subsequent to acquisition	0
TOTAL	0
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	0
COST CAPITALIZED subsequent to acquisition	0
TOTAL	0
PERSONAL PROPERTY	5,500
Gross real estate asset, Total	5,500
Accumulated depreciation	4,686
Encumbrances	$ 0
Owned Property [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	204
LAND 1
INITIAL INVESTMENT	$ 303,990
COST CAPITALIZED subsequent to acquisition	10,408
TOTAL	314,398
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	3,364,856
COST CAPITALIZED subsequent to acquisition	621,470
TOTAL	4,035,057
PERSONAL PROPERTY	10,538
Gross real estate asset, Total	4,359,993
Accumulated depreciation	1,121,102
Encumbrances	$ 129,343
Inpatient Rehab [Member] | Minimum [Member]
Real Estate and Accumulated Depreciation [Line Items]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Date Acquired	Jan. 01, 1994
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Date of Construction	Jan. 01, 1986
Inpatient Rehab [Member] | Maximum [Member]
Real Estate and Accumulated Depreciation [Line Items]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Date Acquired	Dec. 31, 2013
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Date of Construction	Dec. 31, 2013
Other Investments [Member] | Minimum [Member]
Real Estate and Accumulated Depreciation [Line Items]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Date Acquired	Jan. 01, 1993
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Date of Construction	Jan. 01, 1964
Other Investments [Member] | Maximum [Member]
Real Estate and Accumulated Depreciation [Line Items]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Date Acquired	Dec. 31, 2015
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Date of Construction	Dec. 31, 2015
Washington [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	25
LAND 1
INITIAL INVESTMENT	$ 54,446
COST CAPITALIZED subsequent to acquisition	4,119
TOTAL	58,565
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	490,461
COST CAPITALIZED subsequent to acquisition	42,306
TOTAL	532,767
PERSONAL PROPERTY	421
Gross real estate asset, Total	591,753
Accumulated depreciation	88,890
Encumbrances	$ 22,666
Dallas, Texas [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	25
LAND 1
INITIAL INVESTMENT	$ 18,785
COST CAPITALIZED subsequent to acquisition	409
TOTAL	19,194
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	372,644
COST CAPITALIZED subsequent to acquisition	124,039
TOTAL	496,683
PERSONAL PROPERTY	442
Gross real estate asset, Total	516,319
Accumulated depreciation	181,556
Encumbrances	$ 0
Los Angeles, California [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	14
LAND 1
INITIAL INVESTMENT	$ 43,719
COST CAPITALIZED subsequent to acquisition	667
TOTAL	44,386
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	161,322
COST CAPITALIZED subsequent to acquisition	44,507
TOTAL	205,829
PERSONAL PROPERTY	347
Gross real estate asset, Total	250,562
Accumulated depreciation	95,979
Encumbrances	$ 22,340
Georgia [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	9
LAND 1
INITIAL INVESTMENT	$ 3,251
COST CAPITALIZED subsequent to acquisition	428
TOTAL	3,679
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	209,400
COST CAPITALIZED subsequent to acquisition	3,109
TOTAL	212,509
PERSONAL PROPERTY	84
Gross real estate asset, Total	216,272
Accumulated depreciation	20,040
Encumbrances	$ 31,715
Nashville, Tennessee [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	6
LAND 1
INITIAL INVESTMENT	$ 20,004
COST CAPITALIZED subsequent to acquisition	49
TOTAL	20,053
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	115,061
COST CAPITALIZED subsequent to acquisition	65,402
TOTAL	180,463
PERSONAL PROPERTY	1,109
Gross real estate asset, Total	201,625
Accumulated depreciation	64,038
Encumbrances	$ 0
North Carolina [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	16
LAND 1
INITIAL INVESTMENT	$ 4,163
COST CAPITALIZED subsequent to acquisition	37
TOTAL	4,200
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	159,340
COST CAPITALIZED subsequent to acquisition	16,921
TOTAL	176,261
PERSONAL PROPERTY	105
Gross real estate asset, Total	180,566
Accumulated depreciation	67,040
Encumbrances	$ 0
Colorado [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	9
LAND 1
INITIAL INVESTMENT	$ 13,887
COST CAPITALIZED subsequent to acquisition	2,627
TOTAL	16,514
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	106,183
COST CAPITALIZED subsequent to acquisition	27,821
TOTAL	134,004
PERSONAL PROPERTY	271
Gross real estate asset, Total	150,789
Accumulated depreciation	25,265
Encumbrances	$ 7,565
Washington, D.C. [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	6
LAND 1
INITIAL INVESTMENT	$ 0
COST CAPITALIZED subsequent to acquisition	0
TOTAL	0
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	141,467
COST CAPITALIZED subsequent to acquisition	8,837
TOTAL	150,304
PERSONAL PROPERTY	21
Gross real estate asset, Total	150,325
Accumulated depreciation	25,097
Encumbrances	$ 11,707
Virginia [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	7
LAND 1
INITIAL INVESTMENT	$ 0
COST CAPITALIZED subsequent to acquisition	0
TOTAL	0
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	139,636
COST CAPITALIZED subsequent to acquisition	9,496
TOTAL	149,132
PERSONAL PROPERTY	106
Gross real estate asset, Total	149,238
Accumulated depreciation	44,204
Encumbrances	$ 0
Houston, Texas [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	9
LAND 1
INITIAL INVESTMENT	$ 15,475
COST CAPITALIZED subsequent to acquisition	736
TOTAL	16,211
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	107,902
COST CAPITALIZED subsequent to acquisition	24,111
TOTAL	132,013
PERSONAL PROPERTY	78
Gross real estate asset, Total	148,302
Accumulated depreciation	44,229
Encumbrances	$ 0
Hawaii [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	3
LAND 1
INITIAL INVESTMENT	$ 8,314
COST CAPITALIZED subsequent to acquisition	13
TOTAL	8,327
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	93,839
COST CAPITALIZED subsequent to acquisition	41,802
TOTAL	135,641
PERSONAL PROPERTY	159
Gross real estate asset, Total	144,127
Accumulated depreciation	39,165
Encumbrances	$ 0
Iowa [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	7
LAND 1
INITIAL INVESTMENT	$ 12,584
COST CAPITALIZED subsequent to acquisition	81
TOTAL	12,665
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	114,527
COST CAPITALIZED subsequent to acquisition	11,874
TOTAL	126,401
PERSONAL PROPERTY	99
Gross real estate asset, Total	139,165
Accumulated depreciation	34,725
Encumbrances	$ 515
Oklahoma [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	4
LAND 1
INITIAL INVESTMENT	$ 9,838
COST CAPITALIZED subsequent to acquisition	563
TOTAL	10,401
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	114,212
COST CAPITALIZED subsequent to acquisition	1,494
TOTAL	115,706
PERSONAL PROPERTY	15
Gross real estate asset, Total	126,122
Accumulated depreciation	19,351
Encumbrances	$ 5,985
Indiana [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	4
LAND 1
INITIAL INVESTMENT	$ 3,299
COST CAPITALIZED subsequent to acquisition	0
TOTAL	3,299
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	112,718
COST CAPITALIZED subsequent to acquisition	6,129
TOTAL	118,847
PERSONAL PROPERTY	0
Gross real estate asset, Total	122,146
Accumulated depreciation	26,082
Encumbrances	$ 0
San Francisco, California [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	3
LAND 1
INITIAL INVESTMENT	$ 14,054
COST CAPITALIZED subsequent to acquisition	0
TOTAL	14,054
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	93,852
COST CAPITALIZED subsequent to acquisition	13,544
TOTAL	107,396
PERSONAL PROPERTY	43
Gross real estate asset, Total	121,493
Accumulated depreciation	20,906
Encumbrances	$ 0
Missouri [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	1
LAND 1
INITIAL INVESTMENT	$ 1,989
COST CAPITALIZED subsequent to acquisition	0
TOTAL	1,989
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	109,304
COST CAPITALIZED subsequent to acquisition	0
TOTAL	109,304
PERSONAL PROPERTY	0
Gross real estate asset, Total	111,293
Accumulated depreciation	17,740
Encumbrances	$ 0
Austin, Texas [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	5
LAND 1
INITIAL INVESTMENT	$ 14,233
COST CAPITALIZED subsequent to acquisition	3
TOTAL	14,236
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	70,976
COST CAPITALIZED subsequent to acquisition	21,833
TOTAL	92,809
PERSONAL PROPERTY	123
Gross real estate asset, Total	107,168
Accumulated depreciation	24,048
Encumbrances	$ 0
Memphis, Tennessee [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	7
LAND 1
INITIAL INVESTMENT	$ 5,241
COST CAPITALIZED subsequent to acquisition	0
TOTAL	5,241
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	66,868
COST CAPITALIZED subsequent to acquisition	25,640
TOTAL	92,508
PERSONAL PROPERTY	194
Gross real estate asset, Total	97,943
Accumulated depreciation	37,582
Encumbrances	$ 0
San Antonio, Texas [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	6
LAND 1
INITIAL INVESTMENT	$ 6,456
COST CAPITALIZED subsequent to acquisition	31
TOTAL	6,487
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	62,161
COST CAPITALIZED subsequent to acquisition	26,422
TOTAL	88,583
PERSONAL PROPERTY	404
Gross real estate asset, Total	95,474
Accumulated depreciation	40,573
Encumbrances	$ 0
Illinois [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	3
LAND 1
INITIAL INVESTMENT	$ 5,859
COST CAPITALIZED subsequent to acquisition	0
TOTAL	5,859
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	69,993
COST CAPITALIZED subsequent to acquisition	17,595
TOTAL	87,588
PERSONAL PROPERTY	211
Gross real estate asset, Total	93,658
Accumulated depreciation	23,540
Encumbrances	$ 0
Minnesota [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	4
LAND 1
INITIAL INVESTMENT	$ 2,090
COST CAPITALIZED subsequent to acquisition	0
TOTAL	2,090
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	61,078
COST CAPITALIZED subsequent to acquisition	1,281
TOTAL	62,359
PERSONAL PROPERTY	0
Gross real estate asset, Total	64,449
Accumulated depreciation	10,486
Encumbrances	$ 18,907
Other (16 MSAs) [Member] | Real Estate [Member]
Summary of real estate properties
NUMBER OF PROP. | Property	31
LAND 1
INITIAL INVESTMENT	$ 16,434
COST CAPITALIZED subsequent to acquisition	645
TOTAL	17,079
BUILDINGS, IMPROVEMENTS, LEASE INTANGIBLES AND CIP 1
INITIAL INVESTMENT	388,102
COST CAPITALIZED subsequent to acquisition	87,307
TOTAL	475,409
PERSONAL PROPERTY	806
Gross real estate asset, Total	493,294
Accumulated depreciation	165,159
Encumbrances	$ 7,943