Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 1 (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Investments In Real Estate [Line Items]
Total Investment in Real Estate	$ 1,113,651	$ 1,043,106	$ 970,964	$ 782,166
Accumulated Depreciation And Amortization Description [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	1,049,787
Cost Capitalized Subsequent to Initial Investment	63,864
Land	669,351
Building and Improvements	444,300
Total Investment in Real Estate	1,113,651
Accumulated Depreciation and Amortization	165,892
Accumulated Depreciation And Amortization Description [Member] | ALABAMA [Member] | Phenix City [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	1,670
Land	942
Building and Improvements	728
Total Investment in Real Estate	1,670
Accumulated Depreciation and Amortization	$ 25
Date of Initial Leasehold or Acquisition Investment	2019
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Brookland One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,468
Land	149
Building and Improvements	1,319
Total Investment in Real Estate	1,468
Accumulated Depreciation and Amortization	$ 665
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Fayetteville One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,867
Land	1,971
Building and Improvements	896
Total Investment in Real Estate	2,867
Accumulated Depreciation and Amortization	$ 77
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Fayetteville Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,266
Land	1,637
Building and Improvements	629
Total Investment in Real Estate	2,266
Accumulated Depreciation and Amortization	$ 54
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Hope [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,472
Land	999
Building and Improvements	473
Total Investment in Real Estate	1,472
Accumulated Depreciation and Amortization	$ 41
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Jonesboro One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,985
Land	330
Building and Improvements	2,655
Total Investment in Real Estate	2,985
Accumulated Depreciation and Amortization	$ 1,389
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Jonesboro Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 868
Land	173
Building and Improvements	695
Total Investment in Real Estate	868
Accumulated Depreciation and Amortization	$ 364
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Lake Charles One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,468
Land	1,002
Building and Improvements	466
Total Investment in Real Estate	1,468
Accumulated Depreciation and Amortization	$ 40
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Lake Charles Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,069
Land	620
Building and Improvements	449
Total Investment in Real Estate	1,069
Accumulated Depreciation and Amortization	$ 41
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Little Rock [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 978
Land	535
Building and Improvements	443
Total Investment in Real Estate	978
Accumulated Depreciation and Amortization	$ 44
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Little Rock One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,763
Land	497
Building and Improvements	2,266
Total Investment in Real Estate	2,763
Accumulated Depreciation and Amortization	$ 31
Date of Initial Leasehold or Acquisition Investment	2019
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Pine Bluff [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,985
Land	2,166
Building and Improvements	819
Total Investment in Real Estate	2,985
Accumulated Depreciation and Amortization	$ 69
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Rogers [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 927
Land	533
Building and Improvements	394
Total Investment in Real Estate	927
Accumulated Depreciation and Amortization	$ 39
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Sulphur [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 777
Land	375
Building and Improvements	402
Total Investment in Real Estate	777
Accumulated Depreciation and Amortization	$ 41
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | Texarkana [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,592
Land	1,058
Building and Improvements	534
Total Investment in Real Estate	1,592
Accumulated Depreciation and Amortization	$ 49
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Buckeye [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,928
Land	2,334
Building and Improvements	1,594
Total Investment in Real Estate	3,928
Accumulated Depreciation and Amortization	$ 203
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Chandler [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,838
Land	1,261
Building and Improvements	577
Total Investment in Real Estate	1,838
Accumulated Depreciation and Amortization	$ 88
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Gilbert One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,602
Land	796
Building and Improvements	806
Total Investment in Real Estate	1,602
Accumulated Depreciation and Amortization	$ 118
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Gilbert Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,204
Land	1,839
Building and Improvements	1,365
Total Investment in Real Estate	3,204
Accumulated Depreciation and Amortization	$ 186
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Gilbert Three[Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,112
Land	1,593
Building and Improvements	1,519
Total Investment in Real Estate	3,112
Accumulated Depreciation and Amortization	$ 207
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Gilbert Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,448
Land	983
Building and Improvements	465
Total Investment in Real Estate	1,448
Accumulated Depreciation and Amortization	$ 69
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Glendale One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,722
Land	1,178
Building and Improvements	544
Total Investment in Real Estate	1,722
Accumulated Depreciation and Amortization	$ 79
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Mesa One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,185
Land	1,612
Building and Improvements	573
Total Investment in Real Estate	2,185
Accumulated Depreciation and Amortization	$ 83
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Mesa Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,503
Land	839
Building and Improvements	664
Total Investment in Real Estate	1,503
Accumulated Depreciation and Amortization	$ 95
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Mesa Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,169
Land	2,005
Building and Improvements	1,164
Total Investment in Real Estate	3,169
Accumulated Depreciation and Amortization	$ 153
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Peoria [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,331
Land	992
Building and Improvements	339
Total Investment in Real Estate	1,331
Accumulated Depreciation and Amortization	$ 53
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Phoenix One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,415
Land	433
Building and Improvements	1,982
Total Investment in Real Estate	2,415
Accumulated Depreciation and Amortization	$ 229
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Phoenix Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,943
Land	1,311
Building and Improvements	632
Total Investment in Real Estate	1,943
Accumulated Depreciation and Amortization	$ 53
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Phoenix Three[Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,177
Land	1,532
Building and Improvements	645
Total Investment in Real Estate	2,177
Accumulated Depreciation and Amortization	$ 93
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Queen Creek [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,868
Land	1,255
Building and Improvements	1,613
Total Investment in Real Estate	2,868
Accumulated Depreciation and Amortization	$ 224
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | San Tan Valley [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 4,022
Land	2,549
Building and Improvements	1,473
Total Investment in Real Estate	4,022
Accumulated Depreciation and Amortization	$ 208
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Sierra Vista One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,765
Land	269
Building and Improvements	1,496
Total Investment in Real Estate	1,765
Accumulated Depreciation and Amortization	$ 202
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Sierra Vista Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 4,440
Land	1,849
Building and Improvements	2,591
Total Investment in Real Estate	4,440
Accumulated Depreciation and Amortization	$ 318
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Tucson One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,085
Land	1,487
Building and Improvements	598
Total Investment in Real Estate	2,085
Accumulated Depreciation and Amortization	$ 91
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Tucson Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,261
Land	664
Building and Improvements	597
Total Investment in Real Estate	1,261
Accumulated Depreciation and Amortization	$ 85
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Tucson Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,303
Land	590
Building and Improvements	713
Total Investment in Real Estate	1,303
Accumulated Depreciation and Amortization	$ 102
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Tucson Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,301
Land	557
Building and Improvements	744
Total Investment in Real Estate	1,301
Accumulated Depreciation and Amortization	$ 105
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Tucson Five [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,652
Land	2,924
Building and Improvements	728
Total Investment in Real Estate	3,652
Accumulated Depreciation and Amortization	$ 104
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Alhambra [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 6,591
Land	6,078
Building and Improvements	513
Total Investment in Real Estate	6,591
Accumulated Depreciation and Amortization	$ 18
Date of Initial Leasehold or Acquisition Investment	2019
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Bellflower One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,369
Land	910
Building and Improvements	459
Total Investment in Real Estate	1,369
Accumulated Depreciation and Amortization	$ 286
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Benicia One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,224
Land	1,058
Building and Improvements	1,166
Total Investment in Real Estate	2,224
Accumulated Depreciation and Amortization	$ 748
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Chula Vista One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,385
Land	889
Building and Improvements	1,496
Total Investment in Real Estate	2,385
Accumulated Depreciation and Amortization	$ 372
Date of Initial Leasehold or Acquisition Investment	2014
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Coachella One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,235
Land	1,217
Building and Improvements	1,018
Total Investment in Real Estate	2,235
Accumulated Depreciation and Amortization	$ 622
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Cotati One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 6,072
Land	4,008
Building and Improvements	2,064
Total Investment in Real Estate	6,072
Accumulated Depreciation and Amortization	$ 521
Date of Initial Leasehold or Acquisition Investment	2015
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Fillmore One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,354
Land	950
Building and Improvements	404
Total Investment in Real Estate	1,354
Accumulated Depreciation and Amortization	$ 251
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Grass Valley One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,485
Land	853
Building and Improvements	632
Total Investment in Real Estate	1,485
Accumulated Depreciation and Amortization	$ 164
Date of Initial Leasehold or Acquisition Investment	2015
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Harbor City One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 4,442
Land	3,597
Building and Improvements	845
Total Investment in Real Estate	4,442
Accumulated Depreciation and Amortization	$ 33
Date of Initial Leasehold or Acquisition Investment	2019
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Hesperia One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,643
Land	849
Building and Improvements	794
Total Investment in Real Estate	1,643
Accumulated Depreciation and Amortization	$ 467
Date of Initial Leasehold or Acquisition Investment	2007