Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 2 (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Investments In Real Estate [Line Items]
Total Investment in Real Estate	$ 1,043,106	$ 970,964	$ 782,166	$ 783,233
Accumulated Depreciation And Amortization Description [Member] | ARKANSAS [Member] | 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	$ 30
Date of Initial Leasehold or Acquisition Investment	2018
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	$ 615
Date of Initial Leasehold or Acquisition Investment	2007
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	$ 868
Land	173
Building and Improvements	695
Total Investment in Real Estate	868
Accumulated Depreciation and Amortization	$ 338
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	$ 2,266
Land	1,637
Building and Improvements	629
Total Investment in Real Estate	2,266
Accumulated Depreciation and Amortization	$ 23
Date of Initial Leasehold or Acquisition Investment	2018
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	$ 2,985
Land	330
Building and Improvements	2,655
Total Investment in Real Estate	2,985
Accumulated Depreciation and Amortization	$ 1,285
Date of Initial Leasehold or Acquisition Investment	2007
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	$ 2,867
Land	1,971
Building and Improvements	896
Total Investment in Real Estate	2,867
Accumulated Depreciation and Amortization	$ 33
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	$ 18
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	$ 19
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	$ 17
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	$ 21
Date of Initial Leasehold or Acquisition Investment	2018
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	$ 271
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	$ 714
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	$ 299
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	$ 589
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	$ 407
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	$ 238
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	$ 128
Date of Initial Leasehold or Acquisition Investment	2015
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	$ 440
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Hesperia Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,055
Land	492
Building and Improvements	1,563
Total Investment in Real Estate	2,055
Accumulated Depreciation and Amortization	$ 375
Date of Initial Leasehold or Acquisition Investment	2015
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Indio One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,250
Land	302
Building and Improvements	948
Total Investment in Real Estate	1,250
Accumulated Depreciation and Amortization	$ 201
Date of Initial Leasehold or Acquisition Investment	2015
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Indio Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,727
Land	1,486
Building and Improvements	1,241
Total Investment in Real Estate	2,727
Accumulated Depreciation and Amortization	$ 276
Date of Initial Leasehold or Acquisition Investment	2015
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | La Palma One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,971
Land	1,389
Building and Improvements	582
Total Investment in Real Estate	1,971
Accumulated Depreciation and Amortization	$ 339
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | La Puenta [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 7,615
Land	6,405
Building and Improvements	1,210
Total Investment in Real Estate	7,615
Accumulated Depreciation and Amortization	$ 282
Date of Initial Leasehold or Acquisition Investment	2015
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Lakeside [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,715
Land	2,695
Building and Improvements	1,020
Total Investment in Real Estate	3,715
Accumulated Depreciation and Amortization	$ 226
Date of Initial Leasehold or Acquisition Investment	2015
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Cochise 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	$ 133
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Cochise 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	$ 182
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa One [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	$ 30
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Two [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	$ 40
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Three [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	$ 55
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	$ 1,943
Land	1,311
Building and Improvements	632
Total Investment in Real Estate	1,943
Accumulated Depreciation and Amortization	$ 18
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Four [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	$ 68
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Five [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	$ 45
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Six [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	$ 50
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Seven [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	$ 53
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Eight [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	$ 48
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Nine [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	$ 140
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Ten [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	$ 128
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Eleven [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	$ 118
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Twelve [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	$ 87
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Thirteen [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	$ 106
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Maricopa Fourteen [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	$ 116
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Pima One [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	$ 49
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Pima Two [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	$ 60
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Pima 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	$ 58
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Pima Four [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	$ 52
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Pima 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	$ 59
Date of Initial Leasehold or Acquisition Investment	2017