Schedule III - Real Estate and Accumulated Depreciation - Property Summary (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) store
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	930
Debt	$ 2,249,685
Land Initial Cost	1,938,111
Building and Improvements Initial Cost	6,462,425
Adjustments and Costs to Land and Building Subsequent to Acquisition	770,180
Gross carrying amount - Land	1,938,923
Gross carrying amount - Building and improvements	7,231,793
Gross carrying amount - Total	9,170,716
Accumulated Depreciation	1,473,852
Right of use asset - finance lease	$ 8,050
Self storage facilities | AL
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	8
Debt	$ 29,567
Land Initial Cost	7,690
Building and Improvements Initial Cost	42,770
Adjustments and Costs to Land and Building Subsequent to Acquisition	3,693
Gross carrying amount - Land	7,691
Gross carrying amount - Building and improvements	46,462
Gross carrying amount - Total	54,153
Accumulated Depreciation	$ 8,277
Self storage facilities | AZ
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	23
Debt	$ 21,845
Land Initial Cost	27,535
Building and Improvements Initial Cost	117,304
Adjustments and Costs to Land and Building Subsequent to Acquisition	9,574
Gross carrying amount - Land	27,533
Gross carrying amount - Building and improvements	126,880
Gross carrying amount - Total	154,413
Accumulated Depreciation	$ 24,239
Self storage facilities | CA
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	165
Debt	$ 531,406
Land Initial Cost	539,355
Building and Improvements Initial Cost	1,166,591
Adjustments and Costs to Land and Building Subsequent to Acquisition	109,246
Gross carrying amount - Land	540,043
Gross carrying amount - Building and improvements	1,275,149
Gross carrying amount - Total	1,815,192
Accumulated Depreciation	$ 264,874
Self storage facilities | CO
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	16
Debt	$ 30,432
Land Initial Cost	16,809
Building and Improvements Initial Cost	71,894
Adjustments and Costs to Land and Building Subsequent to Acquisition	16,652
Gross carrying amount - Land	17,527
Gross carrying amount - Building and improvements	87,828
Gross carrying amount - Total	105,355
Accumulated Depreciation	$ 19,546
Self storage facilities | CT
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	7
Debt	$ 23,557
Land Initial Cost	9,875
Building and Improvements Initial Cost	50,966
Adjustments and Costs to Land and Building Subsequent to Acquisition	4,766
Gross carrying amount - Land	9,874
Gross carrying amount - Building and improvements	55,733
Gross carrying amount - Total	65,607
Accumulated Depreciation	$ 9,934
Self storage facilities | FL
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	91
Debt	$ 263,634
Land Initial Cost	163,455
Building and Improvements Initial Cost	588,353
Adjustments and Costs to Land and Building Subsequent to Acquisition	56,727
Gross carrying amount - Land	163,919
Gross carrying amount - Building and improvements	644,616
Gross carrying amount - Total	808,535
Accumulated Depreciation	$ 134,121
Self storage facilities | GA
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	63
Debt	$ 85,820
Land Initial Cost	83,742
Building and Improvements Initial Cost	406,477
Adjustments and Costs to Land and Building Subsequent to Acquisition	27,502
Gross carrying amount - Land	83,726
Gross carrying amount - Building and improvements	433,995
Gross carrying amount - Total	517,721
Accumulated Depreciation	$ 60,262
Self storage facilities | HI
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	13
Debt	$ 31,029
Land Initial Cost	17,663
Building and Improvements Initial Cost	133,870
Adjustments and Costs to Land and Building Subsequent to Acquisition	6,025
Gross carrying amount - Land	17,663
Gross carrying amount - Building and improvements	139,895
Gross carrying amount - Total	157,558
Accumulated Depreciation	$ 25,676
Self storage facilities | IL
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	37
Debt	$ 50,669
Land Initial Cost	45,435
Building and Improvements Initial Cost	234,396
Adjustments and Costs to Land and Building Subsequent to Acquisition	25,785
Gross carrying amount - Land	44,888
Gross carrying amount - Building and improvements	260,728
Gross carrying amount - Total	305,616
Accumulated Depreciation	$ 43,160
Self storage facilities | IN
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	15
Debt	$ 10,987
Land Initial Cost	12,447
Building and Improvements Initial Cost	58,247
Adjustments and Costs to Land and Building Subsequent to Acquisition	5,850
Gross carrying amount - Land	12,447
Gross carrying amount - Building and improvements	64,097
Gross carrying amount - Total	76,544
Accumulated Depreciation	$ 11,698
Self storage facilities | KS
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	1
Debt	$ 0
Land Initial Cost	366
Building and Improvements Initial Cost	1,897
Adjustments and Costs to Land and Building Subsequent to Acquisition	866
Gross carrying amount - Land	366
Gross carrying amount - Building and improvements	2,763
Gross carrying amount - Total	3,129
Accumulated Depreciation	$ 1,087
Self storage facilities | KY
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	11
Debt	$ 34,066
Land Initial Cost	8,640
Building and Improvements Initial Cost	68,679
Adjustments and Costs to Land and Building Subsequent to Acquisition	18,260
Gross carrying amount - Land	9,412
Gross carrying amount - Building and improvements	86,167
Gross carrying amount - Total	95,579
Accumulated Depreciation	$ 12,296
Self storage facilities | LA
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	2
Debt	$ 0
Land Initial Cost	6,114
Building and Improvements Initial Cost	8,541
Adjustments and Costs to Land and Building Subsequent to Acquisition	1,312
Gross carrying amount - Land	6,115
Gross carrying amount - Building and improvements	9,852
Gross carrying amount - Total	15,967
Accumulated Depreciation	$ 4,221
Self storage facilities | MA
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	46
Debt	$ 105,046
Land Initial Cost	73,544
Building and Improvements Initial Cost	270,243
Adjustments and Costs to Land and Building Subsequent to Acquisition	50,778
Gross carrying amount - Land	73,725
Gross carrying amount - Building and improvements	320,840
Gross carrying amount - Total	394,565
Accumulated Depreciation	$ 80,863
Self storage facilities | MD
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	32
Debt	$ 118,007
Land Initial Cost	99,147
Building and Improvements Initial Cost	284,253
Adjustments and Costs to Land and Building Subsequent to Acquisition	16,756
Gross carrying amount - Land	97,180
Gross carrying amount - Building and improvements	302,976
Gross carrying amount - Total	400,156
Accumulated Depreciation	$ 70,387
Self storage facilities | MI
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	7
Debt	$ 5,792
Land Initial Cost	9,583
Building and Improvements Initial Cost	51,359
Adjustments and Costs to Land and Building Subsequent to Acquisition	3,239
Gross carrying amount - Land	9,583
Gross carrying amount - Building and improvements	54,598
Gross carrying amount - Total	64,181
Accumulated Depreciation	$ 5,740
Self storage facilities | MN
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	5
Debt	$ 0
Land Initial Cost	7,377
Building and Improvements Initial Cost	50,057
Adjustments and Costs to Land and Building Subsequent to Acquisition	514
Gross carrying amount - Land	7,377
Gross carrying amount - Building and improvements	50,571
Gross carrying amount - Total	57,948
Accumulated Depreciation	$ 2,585
Self storage facilities | MO
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	5
Debt	$ 0
Land Initial Cost	4,129
Building and Improvements Initial Cost	15,444
Adjustments and Costs to Land and Building Subsequent to Acquisition	4,107
Gross carrying amount - Land	4,086
Gross carrying amount - Building and improvements	19,594
Gross carrying amount - Total	23,680
Accumulated Depreciation	$ 7,392
Self storage facilities | MS
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	3
Debt	$ 0
Land Initial Cost	2,420
Building and Improvements Initial Cost	20,849
Adjustments and Costs to Land and Building Subsequent to Acquisition	1,450
Gross carrying amount - Land	2,420
Gross carrying amount - Building and improvements	22,299
Gross carrying amount - Total	24,719
Accumulated Depreciation	$ 2,635
Self storage facilities | NC
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	19
Debt	$ 28,221
Land Initial Cost	31,969
Building and Improvements Initial Cost	104,104
Adjustments and Costs to Land and Building Subsequent to Acquisition	7,379
Gross carrying amount - Land	31,967
Gross carrying amount - Building and improvements	111,485
Gross carrying amount - Total	143,452
Accumulated Depreciation	$ 11,241
Self storage facilities | NH
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	2
Debt	$ 5,938
Land Initial Cost	754
Building and Improvements Initial Cost	4,054
Adjustments and Costs to Land and Building Subsequent to Acquisition	1,278
Gross carrying amount - Land	817
Gross carrying amount - Building and improvements	5,269
Gross carrying amount - Total	6,086
Accumulated Depreciation	$ 2,388
Self storage facilities | NJ
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	59
Debt	$ 155,754
Land Initial Cost	134,032
Building and Improvements Initial Cost	560,512
Adjustments and Costs to Land and Building Subsequent to Acquisition	41,422
Gross carrying amount - Land	137,258
Gross carrying amount - Building and improvements	598,708
Gross carrying amount - Total	735,966
Accumulated Depreciation	$ 129,970
Self storage facilities | NM
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	11
Debt	$ 17,689
Land Initial Cost	32,252
Building and Improvements Initial Cost	71,142
Adjustments and Costs to Land and Building Subsequent to Acquisition	5,049
Gross carrying amount - Land	32,252
Gross carrying amount - Building and improvements	76,191
Gross carrying amount - Total	108,443
Accumulated Depreciation	$ 9,373
Self storage facilities | NV
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	14
Debt	$ 37,557
Land Initial Cost	15,252
Building and Improvements Initial Cost	74,376
Adjustments and Costs to Land and Building Subsequent to Acquisition	4,671
Gross carrying amount - Land	15,252
Gross carrying amount - Building and improvements	79,047
Gross carrying amount - Total	94,299
Accumulated Depreciation	$ 10,422
Self storage facilities | NY
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	27
Debt	$ 43,218
Land Initial Cost	121,945
Building and Improvements Initial Cost	230,875
Adjustments and Costs to Land and Building Subsequent to Acquisition	34,801
Gross carrying amount - Land	122,680
Gross carrying amount - Building and improvements	264,941
Gross carrying amount - Total	387,621
Accumulated Depreciation	$ 59,450
Self storage facilities | OH
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	17
Debt	$ 34,470
Land Initial Cost	17,788
Building and Improvements Initial Cost	50,493
Adjustments and Costs to Land and Building Subsequent to Acquisition	6,733
Gross carrying amount - Land	17,787
Gross carrying amount - Building and improvements	57,227
Gross carrying amount - Total	75,014
Accumulated Depreciation	$ 13,318
Self storage facilities | OR
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	6
Debt	$ 30,267
Land Initial Cost	7,906
Building and Improvements Initial Cost	39,576
Adjustments and Costs to Land and Building Subsequent to Acquisition	2,042
Gross carrying amount - Land	7,906
Gross carrying amount - Building and improvements	41,618
Gross carrying amount - Total	49,524
Accumulated Depreciation	$ 7,545
Self storage facilities | PA
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	18
Debt	$ 34,475
Land Initial Cost	24,297
Building and Improvements Initial Cost	149,144
Adjustments and Costs to Land and Building Subsequent to Acquisition	12,297
Gross carrying amount - Land	23,589
Gross carrying amount - Building and improvements	162,149
Gross carrying amount - Total	185,738
Accumulated Depreciation	$ 24,480
Self storage facilities | RI
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	2
Debt	$ 11,841
Land Initial Cost	3,191
Building and Improvements Initial Cost	6,926
Adjustments and Costs to Land and Building Subsequent to Acquisition	1,253
Gross carrying amount - Land	3,191
Gross carrying amount - Building and improvements	8,179
Gross carrying amount - Total	11,370
Accumulated Depreciation	$ 2,939
Self storage facilities | SC
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	23
Debt	$ 43,543
Land Initial Cost	37,075
Building and Improvements Initial Cost	135,760
Adjustments and Costs to Land and Building Subsequent to Acquisition	10,029
Gross carrying amount - Land	37,076
Gross carrying amount - Building and improvements	145,788
Gross carrying amount - Total	182,864
Accumulated Depreciation	$ 22,598
Self storage facilities | TN
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	17
Debt	$ 45,601
Land Initial Cost	25,938
Building and Improvements Initial Cost	91,497
Adjustments and Costs to Land and Building Subsequent to Acquisition	8,750
Gross carrying amount - Land	25,938
Gross carrying amount - Building and improvements	100,247
Gross carrying amount - Total	126,185
Accumulated Depreciation	$ 18,046
Self storage facilities | TX
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	100
Debt	$ 213,291
Land Initial Cost	169,160
Building and Improvements Initial Cost	648,128
Adjustments and Costs to Land and Building Subsequent to Acquisition	57,365
Gross carrying amount - Land	169,012
Gross carrying amount - Building and improvements	705,641
Gross carrying amount - Total	874,653
Accumulated Depreciation	$ 112,790
Self storage facilities | UT
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	10
Debt	$ 13,181
Land Initial Cost	9,008
Building and Improvements Initial Cost	39,295
Adjustments and Costs to Land and Building Subsequent to Acquisition	2,247
Gross carrying amount - Land	9,008
Gross carrying amount - Building and improvements	41,542
Gross carrying amount - Total	50,550
Accumulated Depreciation	$ 9,854
Self storage facilities | VA
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	46
Debt	$ 163,675
Land Initial Cost	139,318
Building and Improvements Initial Cost	414,335
Adjustments and Costs to Land and Building Subsequent to Acquisition	19,385
Gross carrying amount - Land	139,319
Gross carrying amount - Building and improvements	433,719
Gross carrying amount - Total	573,038
Accumulated Depreciation	$ 69,063
Self storage facilities | DC
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	8
Debt	$ 20,345
Land Initial Cost	12,528
Building and Improvements Initial Cost	47,645
Adjustments and Costs to Land and Building Subsequent to Acquisition	2,694
Gross carrying amount - Land	12,530
Gross carrying amount - Building and improvements	50,337
Gross carrying amount - Total	62,867
Accumulated Depreciation	$ 11,380
Self storage facilities | DC
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Store Count | store	1
Debt	$ 8,762
Land Initial Cost	14,394
Building and Improvements Initial Cost	18,172
Adjustments and Costs to Land and Building Subsequent to Acquisition	429
Gross carrying amount - Land	14,394
Gross carrying amount - Building and improvements	18,601
Gross carrying amount - Total	32,995
Accumulated Depreciation	1,824
Other corporate assets
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Debt	0
Land Initial Cost	0
Building and Improvements Initial Cost	2,202
Adjustments and Costs to Land and Building Subsequent to Acquisition	138,483
Gross carrying amount - Land	0
Gross carrying amount - Building and improvements	140,685
Gross carrying amount - Total	140,685
Accumulated Depreciation	40,298
Intangible tenant relationships and lease rights
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Debt	0
Land Initial Cost	0
Building and Improvements Initial Cost	132,000
Adjustments and Costs to Land and Building Subsequent to Acquisition	2,932
Gross carrying amount - Land	0
Gross carrying amount - Building and improvements	134,932
Gross carrying amount - Total	134,932
Accumulated Depreciation	127,712
Construction in Progress/Undeveloped Land
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Debt	0
Land Initial Cost	5,978
Building and Improvements Initial Cost	0
Adjustments and Costs to Land and Building Subsequent to Acquisition	39,788
Gross carrying amount - Land	3,372
Gross carrying amount - Building and improvements	42,394
Gross carrying amount - Total	45,766
Accumulated Depreciation	0
Right of use asset - finance lease
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Debt	0
Land Initial Cost	0
Building and Improvements Initial Cost	0
Adjustments and Costs to Land and Building Subsequent to Acquisition	8,050
Gross carrying amount - Land	0
Gross carrying amount - Building and improvements	8,050
Gross carrying amount - Total	8,050
Accumulated Depreciation	$ 168