Schedule III - Real Estate and Accumulated Depreciation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) property Property	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Summary of real estate properties
Number of Properties | property	199
Buildings, Improvements, Lease Intangibles and CIP (1)
Gross real estate asset, Total	$ 3,993,427	$ 3,907,010	$ 3,633,993	$ 3,382,680
Accumulated depreciation	$ 1,025,831	$ 933,220	$ 843,816	$ 762,996
Medical office/outpatient [Member] | Minimum [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Date Acquired	Jan. 01, 1993
Date Constructed	Jan. 01, 1906
Medical office/outpatient [Member] | Maximum [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Date Acquired	Dec. 31, 2017
Date Constructed	Dec. 31, 2015
Inpatient [Member] | Minimum [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Date Acquired	Jan. 01, 1994
Date Constructed	Jan. 01, 1986
Inpatient [Member] | Maximum [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Date Acquired	Dec. 31, 2013
Date Constructed	Dec. 31, 2013
Other [Member] | Minimum [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Date Acquired	Jan. 01, 1993
Date Constructed	Jan. 01, 1964
Other [Member] | Maximum [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Date Acquired	Dec. 31, 2015
Date Constructed	Dec. 31, 2015
Real Estate [Member]
Summary of real estate properties
Number of Properties | Property	200
Land (1)
Initial Investment	$ 224,504
Cost Capitalized Subsequent to Acquisition	6,827
Total	231,331
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	3,123,655
Cost Capitalized Subsequent to Acquisition	569,991
Total	3,693,646
Personal Property	5,196
Gross real estate asset, Total	3,930,173
Accumulated depreciation	1,020,971
Encumbrances	$ 143,208
Land Held for Development [Member]
Summary of real estate properties
Number of Properties | 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	393
Encumbrances	0
Construction in Progress [Member]
Buildings, Improvements, Lease Intangibles and CIP (1)
Total	33,107
Gross real estate asset, Total	$ 33,107
Corporate Property [Member]
Summary of real estate properties
Number of Properties | 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	4,467
Encumbrances	$ 0
Owned Property [Member]
Summary of real estate properties
Number of Properties | Property	200
Land (1)
Initial Investment	$ 249,151
Cost Capitalized Subsequent to Acquisition	6,827
Total	255,978
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	3,123,655
Cost Capitalized Subsequent to Acquisition	569,991
Total	3,726,753
Personal Property	10,696
Gross real estate asset, Total	3,993,427
Accumulated depreciation	1,025,831
Encumbrances	$ 143,208
Dallas, Texas [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | Property	25
Land (1)
Initial Investment	$ 16,668
Cost Capitalized Subsequent to Acquisition	243
Total	16,911
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	345,126
Cost Capitalized Subsequent to Acquisition	118,951
Total	464,077
Personal Property	430
Gross real estate asset, Total	481,418
Accumulated depreciation	166,980
Encumbrances	$ 0
Washington [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | Property	19
Land (1)
Initial Investment	$ 27,050
Cost Capitalized Subsequent to Acquisition	1,817
Total	28,867
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	407,491
Cost Capitalized Subsequent to Acquisition	31,389
Total	438,880
Personal Property	419
Gross real estate asset, Total	468,166
Accumulated depreciation	69,148
Encumbrances	$ 31,868
Nashville, Tennessee [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | 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	61,196
Total	176,257
Personal Property	1,041
Gross real estate asset, Total	197,351
Accumulated depreciation	53,052
Encumbrances	$ 0
Georgia [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | Property	8
Land (1)
Initial Investment	$ 588
Cost Capitalized Subsequent to Acquisition	427
Total	1,015
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	187,088
Cost Capitalized Subsequent to Acquisition	2,079
Total	189,167
Personal Property	37
Gross real estate asset, Total	190,219
Accumulated depreciation	11,547
Encumbrances	$ 32,597
Los Angeles, California [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | Property	12
Land (1)
Initial Investment	$ 27,281
Cost Capitalized Subsequent to Acquisition	428
Total	27,709
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	117,144
Cost Capitalized Subsequent to Acquisition	40,352
Total	157,496
Personal Property	316
Gross real estate asset, Total	185,521
Accumulated depreciation	87,678
Encumbrances	$ 23,103
North Carolina [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | 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	150,022
Cost Capitalized Subsequent to Acquisition	12,900
Total	162,922
Personal Property	99
Gross real estate asset, Total	167,221
Accumulated depreciation	60,389
Encumbrances	$ 0
Colorado [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | 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	108,206
Cost Capitalized Subsequent to Acquisition	23,554
Total	131,760
Personal Property	273
Gross real estate asset, Total	148,547
Accumulated depreciation	20,315
Encumbrances	$ 7,789
Virginia [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | 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	8,173
Total	147,809
Personal Property	106
Gross real estate asset, Total	147,915
Accumulated depreciation	38,288
Encumbrances	$ 0
Hawaii [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | 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	40,198
Total	134,037
Personal Property	159
Gross real estate asset, Total	142,523
Accumulated depreciation	34,703
Encumbrances	$ 0
Iowa [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | 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	116,647
Cost Capitalized Subsequent to Acquisition	10,416
Total	127,063
Personal Property	99
Gross real estate asset, Total	139,827
Accumulated depreciation	30,376
Encumbrances	$ 1,262
Houston, Texas [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | Property	8
Land (1)
Initial Investment	$ 13,408
Cost Capitalized Subsequent to Acquisition	264
Total	13,672
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	96,894
Cost Capitalized Subsequent to Acquisition	22,024
Total	118,918
Personal Property	77
Gross real estate asset, Total	132,667
Accumulated depreciation	39,195
Encumbrances	$ 0
Oklahoma [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | Property	3
Land (1)
Initial Investment	$ 9,077
Cost Capitalized Subsequent to Acquisition	350
Total	9,427
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	111,043
Cost Capitalized Subsequent to Acquisition	409
Total	111,452
Personal Property	10
Gross real estate asset, Total	120,889
Accumulated depreciation	14,751
Encumbrances	$ 6,225
San Francisco, California [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | 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	11,759
Total	105,611
Personal Property	43
Gross real estate asset, Total	119,708
Accumulated depreciation	15,539
Encumbrances	$ 0
Missouri [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | 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	14,893
Encumbrances	$ 0
Austin, Texas [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | 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	20,840
Total	91,816
Personal Property	119
Gross real estate asset, Total	106,171
Accumulated depreciation	20,766
Encumbrances	$ 0
Washington, D.C. [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | Property	4
Land (1)
Initial Investment	$ 0
Cost Capitalized Subsequent to Acquisition	0
Total	0
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	93,730
Cost Capitalized Subsequent to Acquisition	7,456
Total	101,186
Personal Property	8
Gross real estate asset, Total	101,194
Accumulated depreciation	20,701
Encumbrances	$ 11,980
Memphis, Tennessee [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | 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	68,180
Cost Capitalized Subsequent to Acquisition	22,786
Total	90,966
Personal Property	191
Gross real estate asset, Total	96,398
Accumulated depreciation	35,109
Encumbrances	$ 0
San Antonio, Texas [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | Property	7
Land (1)
Initial Investment	$ 6,617
Cost Capitalized Subsequent to Acquisition	30
Total	6,647
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	62,760
Cost Capitalized Subsequent to Acquisition	26,194
Total	88,954
Personal Property	378
Gross real estate asset, Total	95,979
Accumulated depreciation	37,877
Encumbrances	$ 0
Illinois [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | 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	69,964
Cost Capitalized Subsequent to Acquisition	16,104
Total	86,068
Personal Property	201
Gross real estate asset, Total	92,128
Accumulated depreciation	19,372
Encumbrances	$ 0
Indiana [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | Property	3
Land (1)
Initial Investment	$ 3,299
Cost Capitalized Subsequent to Acquisition	0
Total	3,299
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	68,994
Cost Capitalized Subsequent to Acquisition	3,366
Total	72,360
Personal Property	0
Gross real estate asset, Total	75,659
Accumulated depreciation	21,299
Encumbrances	$ 0
Minnesota [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | 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	683
Total	61,761
Personal Property	0
Gross real estate asset, Total	63,851
Accumulated depreciation	7,750
Encumbrances	$ 19,576
Other (21 MSAs) [Member] | Real Estate [Member]
Summary of real estate properties
Number of Properties | Property	40
Land (1)
Initial Investment	$ 18,098
Cost Capitalized Subsequent to Acquisition	458
Total	18,556
Buildings, Improvements, Lease Intangibles and CIP (1)
Initial Investment	436,620
Cost Capitalized Subsequent to Acquisition	89,162
Total	525,782
Personal Property	1,190
Gross real estate asset, Total	545,528
Accumulated depreciation	201,243
Encumbrances	$ 8,808