Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 1 (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Investments In Real Estate [Line Items]
Total Investment in Real Estate	$ 970,964	$ 782,166	$ 783,233	$ 595,959
Accumulated Depreciation And Amortization Description [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	914,488
Cost Capitalized Subsequent to Initial Investment	56,476
Land	589,497
Building and Improvements	381,467
Total Investment in Real Estate	970,964
Accumulated Depreciation and Amortization	133,353
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	$ 564
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	$ 313
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	$ 2,985
Land	330
Building and Improvements	2,655
Total Investment in Real Estate	2,985
Accumulated Depreciation and Amortization	$ 1,181
Date of Initial Leasehold or Acquisition Investment	2007
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	$ 29
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	$ 13
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	$ 1,448
Land	983
Building and Improvements	465
Total Investment in Real Estate	1,448
Accumulated Depreciation and Amortization	$ 10
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	$ 1,602
Land	796
Building and Improvements	806
Total Investment in Real Estate	1,602
Accumulated Depreciation and Amortization	$ 17
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	$ 30
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	$ 3,204
Land	1,839
Building and Improvements	1,365
Total Investment in Real Estate	3,204
Accumulated Depreciation and Amortization	$ 27
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	$ 1,331
Land	992
Building and Improvements	339
Total Investment in Real Estate	1,331
Accumulated Depreciation and Amortization	$ 8
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | Glendale Two [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	$ 11
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	$ 1,503
Land	839
Building and Improvements	664
Total Investment in Real Estate	1,503
Accumulated Depreciation and Amortization	$ 14
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	$ 2,185
Land	1,612
Building and Improvements	573
Total Investment in Real Estate	2,185
Accumulated Depreciation and Amortization	$ 12
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	$ 22
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	$ 2,177
Land	1,532
Building and Improvements	645
Total Investment in Real Estate	2,177
Accumulated Depreciation and Amortization	$ 13
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	$ 2,415
Land	433
Building and Improvements	1,982
Total Investment in Real Estate	2,415
Accumulated Depreciation and Amortization	$ 52
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	$ 32
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | ARIZONA [Member] | SanTan 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	$ 30
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	$ 63
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	$ 45
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	$ 1,261
Land	664
Building and Improvements	597
Total Investment in Real Estate	1,261
Accumulated Depreciation and Amortization	$ 12
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	$ 1,301
Land	557
Building and Improvements	744
Total Investment in Real Estate	1,301
Accumulated Depreciation and Amortization	$ 15
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	$ 15
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	$ 2,085
Land	1,487
Building and Improvements	598
Total Investment in Real Estate	2,085
Accumulated Depreciation and Amortization	$ 13
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	$ 15
Date of Initial Leasehold or Acquisition Investment	2017
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	$ 257
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	$ 679
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	$ 226
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	$ 557
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	$ 294
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	$ 226
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	$ 93
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	$ 413
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	$ 270
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	$ 145
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	$ 199
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	$ 320
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | La Puente One [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	$ 203
Date of Initial Leasehold or Acquisition Investment	2015
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Lakeside One [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	$ 163
Date of Initial Leasehold or Acquisition Investment	2015
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Los Angeles One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 6,612
Land	5,006
Building and Improvements	1,606
Total Investment in Real Estate	6,612
Accumulated Depreciation and Amortization	$ 267
Date of Initial Leasehold or Acquisition Investment	2015
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Oakland One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 5,434
Land	4,123
Building and Improvements	1,311
Total Investment in Real Estate	5,434
Accumulated Depreciation and Amortization	$ 215
Date of Initial Leasehold or Acquisition Investment	2015
Accumulated Depreciation And Amortization Description [Member] | CALIFORNIA [Member] | Ontario One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 6,613
Land	4,523
Building and Improvements	2,090
Total Investment in Real Estate	6,613
Accumulated Depreciation and Amortization	$ 348
Date of Initial Leasehold or Acquisition Investment	2015