Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 12 (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] | SOUTH CAROLINA | Columbia Twelve [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	2,109
Land	1,120
Building and Improvements	989
Total Investment in Real Estate	2,109
Accumulated Depreciation and Amortization	$ 79
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Columbia Thirteen [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,531
Land	1,612
Building and Improvements	919
Total Investment in Real Estate	2,531
Accumulated Depreciation and Amortization	$ 72
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Elgin One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,082
Land	1,166
Building and Improvements	916
Total Investment in Real Estate	2,082
Accumulated Depreciation and Amortization	$ 122
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Elgin Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,177
Land	974
Building and Improvements	1,203
Total Investment in Real Estate	2,177
Accumulated Depreciation and Amortization	$ 151
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Gaston One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,230
Land	934
Building and Improvements	1,296
Total Investment in Real Estate	2,230
Accumulated Depreciation and Amortization	$ 165
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Gilbert One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,036
Land	434
Building and Improvements	602
Total Investment in Real Estate	1,036
Accumulated Depreciation and Amortization	$ 76
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Irmo One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,655
Land	1,742
Building and Improvements	1,913
Total Investment in Real Estate	3,655
Accumulated Depreciation and Amortization	$ 240
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Irmo Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,114
Land	667
Building and Improvements	447
Total Investment in Real Estate	1,114
Accumulated Depreciation and Amortization	$ 57
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Irmo Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,339
Land	867
Building and Improvements	472
Total Investment in Real Estate	1,339
Accumulated Depreciation and Amortization	$ 62
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Irmo Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,246
Land	69
Building and Improvements	1,177
Total Investment in Real Estate	1,246
Accumulated Depreciation and Amortization	$ 141
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Irmo Five [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,950
Land	2,802
Building and Improvements	1,148
Total Investment in Real Estate	3,950
Accumulated Depreciation and Amortization	$ 151
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Johns Island [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,561
Land	1,885
Building and Improvements	676
Total Investment in Real Estate	2,561
Accumulated Depreciation and Amortization	$ 42
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,624
Land	999
Building and Improvements	625
Total Investment in Real Estate	1,624
Accumulated Depreciation and Amortization	$ 81
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 4,413
Land	3,418
Building and Improvements	995
Total Investment in Real Estate	4,413
Accumulated Depreciation and Amortization	$ 145
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 973
Land	582
Building and Improvements	391
Total Investment in Real Estate	973
Accumulated Depreciation and Amortization	$ 54
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,179
Land	1,476
Building and Improvements	703
Total Investment in Real Estate	2,179
Accumulated Depreciation and Amortization	$ 91
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Five [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 633
Land	309
Building and Improvements	324
Total Investment in Real Estate	633
Accumulated Depreciation and Amortization	$ 43
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Six [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,729
Land	1,268
Building and Improvements	461
Total Investment in Real Estate	1,729
Accumulated Depreciation and Amortization	$ 69
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Seven [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 694
Land	172
Building and Improvements	522
Total Investment in Real Estate	694
Accumulated Depreciation and Amortization	$ 74
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Eight [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,056
Land	432
Building and Improvements	624
Total Investment in Real Estate	1,056
Accumulated Depreciation and Amortization	$ 85
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Nine [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 720
Land	219
Building and Improvements	501
Total Investment in Real Estate	720
Accumulated Depreciation and Amortization	$ 64
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Ten [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,738
Land	1,189
Building and Improvements	549
Total Investment in Real Estate	1,738
Accumulated Depreciation and Amortization	$ 56
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Eleven [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 816
Land	336
Building and Improvements	480
Total Investment in Real Estate	816
Accumulated Depreciation and Amortization	$ 48
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Twelve [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,712
Land	1,410
Building and Improvements	302
Total Investment in Real Estate	1,712
Accumulated Depreciation and Amortization	$ 34
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Thirteen [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,603
Land	1,869
Building and Improvements	734
Total Investment in Real Estate	2,603
Accumulated Depreciation and Amortization	$ 64
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Fourteen [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,231
Land	2,001
Building and Improvements	1,230
Total Investment in Real Estate	3,231
Accumulated Depreciation and Amortization	$ 102
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Lexington Fifteen [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,234
Land	1,198
Building and Improvements	2,036
Total Investment in Real Estate	3,234
Accumulated Depreciation and Amortization	$ 154
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | Pelion One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,901
Land	1,021
Building and Improvements	880
Total Investment in Real Estate	1,901
Accumulated Depreciation and Amortization	$ 132
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | West Columbia One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,644
Land	1,283
Building and Improvements	361
Total Investment in Real Estate	1,644
Accumulated Depreciation and Amortization	$ 49
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | West Columbia Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,046
Land	746
Building and Improvements	1,300
Total Investment in Real Estate	2,046
Accumulated Depreciation and Amortization	$ 162
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | SOUTH CAROLINA | West Columbia Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,116
Land	50
Building and Improvements	1,066
Total Investment in Real Estate	1,116
Accumulated Depreciation and Amortization	$ 139
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | TEXAS | Arlington One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,796
Land	1,189
Building and Improvements	607
Total Investment in Real Estate	1,796
Accumulated Depreciation and Amortization	$ 53
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | TEXAS | Arlington Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,560
Land	1,008
Building and Improvements	552
Total Investment in Real Estate	1,560
Accumulated Depreciation and Amortization	$ 47
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | TEXAS | Arlington Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,352
Land	887
Building and Improvements	465
Total Investment in Real Estate	1,352
Accumulated Depreciation and Amortization	$ 42
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | TEXAS | Arlington Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 789
Land	414
Building and Improvements	375
Total Investment in Real Estate	789
Accumulated Depreciation and Amortization	$ 36
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | TEXAS | Austin One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,368
Land	738
Building and Improvements	1,630
Total Investment in Real Estate	2,368
Accumulated Depreciation and Amortization	$ 911
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | TEXAS | Austin Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 462
Land	274
Building and Improvements	188
Total Investment in Real Estate	462
Accumulated Depreciation and Amortization	$ 134
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | TEXAS | Austin Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,511
Cost Capitalized Subsequent to Initial Investment	66
Land	1,595
Building and Improvements	1,982
Total Investment in Real Estate	3,577
Accumulated Depreciation and Amortization	$ 1,083
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | TEXAS | Austin Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,711
Land	1,364
Building and Improvements	347
Total Investment in Real Estate	1,711
Accumulated Depreciation and Amortization	$ 55
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | TEXAS | Center [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,073
Land	1,482
Building and Improvements	591
Total Investment in Real Estate	2,073
Accumulated Depreciation and Amortization	$ 57
Date of Initial Leasehold or Acquisition Investment	2018
Accumulated Depreciation And Amortization Description [Member] | TEXAS | Corpus Christi One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,162
Land	1,729
Building and Improvements	433
Total Investment in Real Estate	2,162
Accumulated Depreciation and Amortization	$ 65
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | TEXAS | Corpus Christi Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,526
Land	1,056
Building and Improvements	470
Total Investment in Real Estate	1,526
Accumulated Depreciation and Amortization	$ 63
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | TEXAS | Corpus Christi Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,400
Land	1,110
Building and Improvements	1,290
Total Investment in Real Estate	2,400
Accumulated Depreciation and Amortization	$ 173
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | TEXAS | El Paso One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,425
Land	1,098
Building and Improvements	327
Total Investment in Real Estate	1,425
Accumulated Depreciation and Amortization	$ 50
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | TEXAS | El Paso Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,168
Land	2,153
Building and Improvements	1,015
Total Investment in Real Estate	3,168
Accumulated Depreciation and Amortization	$ 140
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | TEXAS | El Paso Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,278
Land	825
Building and Improvements	453
Total Investment in Real Estate	1,278
Accumulated Depreciation and Amortization	$ 67
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | TEXAS | El Paso Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,816
Land	1,413
Building and Improvements	403
Total Investment in Real Estate	1,816
Accumulated Depreciation and Amortization	$ 61
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | TEXAS | El Paso Five [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,370
Land	1,767
Building and Improvements	603
Total Investment in Real Estate	2,370
Accumulated Depreciation and Amortization	$ 83
Date of Initial Leasehold or Acquisition Investment	2017