Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 14 (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
NEW HAMPSHIRE [Member] | Accumulated Depreciation And Amortization Description [Member] | Salem One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	743
Cost Capitalized Subsequent to Initial Investment	20
Land	484
Building and Improvements	279
Total Investment in Real Estate	763
Accumulated Depreciation and Amortization	$ 236
Date of Initial Leasehold or Acquisition Investment	1985
NEW HAMPSHIRE [Member] | Accumulated Depreciation And Amortization Description [Member] | Salem Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 450
Cost Capitalized Subsequent to Initial Investment	871
Land	350
Building and Improvements	971
Total Investment in Real Estate	1,321
Accumulated Depreciation and Amortization	$ 122
Date of Initial Leasehold or Acquisition Investment	1986
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Basking Ridge One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 363
Cost Capitalized Subsequent to Initial Investment	284
Land	200
Building and Improvements	447
Total Investment in Real Estate	647
Accumulated Depreciation and Amortization	$ 278
Date of Initial Leasehold or Acquisition Investment	1986
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Bergenfield One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 381
Cost Capitalized Subsequent to Initial Investment	323
Land	300
Building and Improvements	404
Total Investment in Real Estate	704
Accumulated Depreciation and Amortization	$ 225
Date of Initial Leasehold or Acquisition Investment	1990
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Brick One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,508
Cost Capitalized Subsequent to Initial Investment	229
Land	1,000
Building and Improvements	737
Total Investment in Real Estate	1,737
Accumulated Depreciation and Amortization	$ 509
Date of Initial Leasehold or Acquisition Investment	2000
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Colonia One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 719
Cost Capitalized Subsequent to Initial Investment	(299)
Land	72
Building and Improvements	348
Total Investment in Real Estate	420
Accumulated Depreciation and Amortization	$ 282
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Elizabeth One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 406
Cost Capitalized Subsequent to Initial Investment	33
Land	227
Building and Improvements	212
Total Investment in Real Estate	439
Accumulated Depreciation and Amortization	$ 188
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Flemington One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 709
Cost Capitalized Subsequent to Initial Investment	(252)
Land	168
Building and Improvements	289
Total Investment in Real Estate	457
Accumulated Depreciation and Amortization	$ 120
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Flemington Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 547
Cost Capitalized Subsequent to Initial Investment	17
Land	346
Building and Improvements	218
Total Investment in Real Estate	564
Accumulated Depreciation and Amortization	$ 185
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Fort Lee One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,245
Cost Capitalized Subsequent to Initial Investment	365
Land	811
Building and Improvements	799
Total Investment in Real Estate	1,610
Accumulated Depreciation and Amortization	$ 538
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Franklin Twp One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 684
Cost Capitalized Subsequent to Initial Investment	169
Land	445
Building and Improvements	408
Total Investment in Real Estate	853
Accumulated Depreciation and Amortization	$ 352
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Freehold One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 495
Cost Capitalized Subsequent to Initial Investment	533
Land	95
Building and Improvements	933
Total Investment in Real Estate	1,028
Accumulated Depreciation and Amortization	$ 170
Date of Initial Leasehold or Acquisition Investment	1978
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Hasbrouck Heights One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 640
Cost Capitalized Subsequent to Initial Investment	483
Land	416
Building and Improvements	707
Total Investment in Real Estate	1,123
Accumulated Depreciation and Amortization	$ 449
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Hillsborough One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 238
Cost Capitalized Subsequent to Initial Investment	182
Land	100
Building and Improvements	320
Total Investment in Real Estate	420
Accumulated Depreciation and Amortization	$ 245
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Lake Hopatcong One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,305
Land	800
Building and Improvements	505
Total Investment in Real Estate	1,305
Accumulated Depreciation and Amortization	$ 436
Date of Initial Leasehold or Acquisition Investment	2000
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Livingston One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 872
Cost Capitalized Subsequent to Initial Investment	292
Land	568
Building and Improvements	596
Total Investment in Real Estate	1,164
Accumulated Depreciation and Amortization	$ 391
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Long Branch One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 515
Cost Capitalized Subsequent to Initial Investment	439
Land	335
Building and Improvements	619
Total Investment in Real Estate	954
Accumulated Depreciation and Amortization	$ 323
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Mcafee One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 671
Cost Capitalized Subsequent to Initial Investment	448
Land	437
Building and Improvements	682
Total Investment in Real Estate	1,119
Accumulated Depreciation and Amortization	$ 342
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Midland Park One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 201
Cost Capitalized Subsequent to Initial Investment	309
Land	150
Building and Improvements	360
Total Investment in Real Estate	510
Accumulated Depreciation and Amortization	$ 208
Date of Initial Leasehold or Acquisition Investment	1989
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Mountainside One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 664
Cost Capitalized Subsequent to Initial Investment	(197)
Land	134
Building and Improvements	333
Total Investment in Real Estate	467
Accumulated Depreciation and Amortization	$ 152
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | North Bergen One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 630
Cost Capitalized Subsequent to Initial Investment	147
Land	410
Building and Improvements	367
Total Investment in Real Estate	777
Accumulated Depreciation and Amortization	$ 296
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | North Plainfield One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 227
Cost Capitalized Subsequent to Initial Investment	544
Land	175
Building and Improvements	596
Total Investment in Real Estate	771
Accumulated Depreciation and Amortization	$ 448
Date of Initial Leasehold or Acquisition Investment	1978
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Paramus One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 382
Cost Capitalized Subsequent to Initial Investment	81
Land	249
Building and Improvements	214
Total Investment in Real Estate	463
Accumulated Depreciation and Amortization	$ 150
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Parlin [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 418
Cost Capitalized Subsequent to Initial Investment	159
Land	203
Building and Improvements	374
Total Investment in Real Estate	577
Accumulated Depreciation and Amortization	$ 158
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Paterson One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 619
Cost Capitalized Subsequent to Initial Investment	17
Land	403
Building and Improvements	233
Total Investment in Real Estate	636
Accumulated Depreciation and Amortization	$ 198
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Ridgewood [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 703
Cost Capitalized Subsequent to Initial Investment	398
Land	458
Building and Improvements	643
Total Investment in Real Estate	1,101
Accumulated Depreciation and Amortization	$ 395
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Trenton One
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,303
Land	1,146
Building and Improvements	157
Total Investment in Real Estate	1,303
Accumulated Depreciation and Amortization	$ 58
Date of Initial Leasehold or Acquisition Investment	2012
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Union One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 437
Cost Capitalized Subsequent to Initial Investment	214
Land	239
Building and Improvements	412
Total Investment in Real Estate	651
Accumulated Depreciation and Amortization	$ 192
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Washington One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 912
Cost Capitalized Subsequent to Initial Investment	334
Land	594
Building and Improvements	652
Total Investment in Real Estate	1,246
Accumulated Depreciation and Amortization	$ 394
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Watchung One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 449
Cost Capitalized Subsequent to Initial Investment	114
Land	226
Building and Improvements	337
Total Investment in Real Estate	563
Accumulated Depreciation and Amortization	$ 140
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | West Orange One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 800
Cost Capitalized Subsequent to Initial Investment	409
Land	521
Building and Improvements	688
Total Investment in Real Estate	1,209
Accumulated Depreciation and Amortization	$ 475
Date of Initial Leasehold or Acquisition Investment	1985
NEW MEXICO [Member] | Accumulated Depreciation And Amortization Description [Member] | Bernalillo One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,829
Land	1,382
Building and Improvements	447
Total Investment in Real Estate	1,829
Accumulated Depreciation and Amortization	$ 37
Date of Initial Leasehold or Acquisition Investment	2017
NEW MEXICO [Member] | Accumulated Depreciation And Amortization Description [Member] | Bernalillo Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,308
Land	1,830
Building and Improvements	478
Total Investment in Real Estate	2,308
Accumulated Depreciation and Amortization	$ 43
Date of Initial Leasehold or Acquisition Investment	2017
NEW MEXICO [Member] | Accumulated Depreciation And Amortization Description [Member] | Bernalillo Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,322
Land	1,796
Building and Improvements	526
Total Investment in Real Estate	2,322
Accumulated Depreciation and Amortization	$ 45
Date of Initial Leasehold or Acquisition Investment	2017
NEW MEXICO [Member] | Accumulated Depreciation And Amortization Description [Member] | Bernalillo Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,682
Land	3,141
Building and Improvements	541
Total Investment in Real Estate	3,682
Accumulated Depreciation and Amortization	$ 48
Date of Initial Leasehold or Acquisition Investment	2017
NEW MEXICO [Member] | Accumulated Depreciation And Amortization Description [Member] | Dona Ana [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,842
Land	1,374
Building and Improvements	468
Total Investment in Real Estate	1,842
Accumulated Depreciation and Amortization	$ 40
Date of Initial Leasehold or Acquisition Investment	2017
NEVADA [Member] | Accumulated Depreciation And Amortization Description [Member] | Fernley One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,665
Land	221
Building and Improvements	1,444
Total Investment in Real Estate	1,665
Accumulated Depreciation and Amortization	$ 366
Date of Initial Leasehold or Acquisition Investment	2015
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Alfred Station One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 714
Land	414
Building and Improvements	300
Total Investment in Real Estate	714
Accumulated Depreciation and Amortization	$ 154
Date of Initial Leasehold or Acquisition Investment	2006
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Amherst One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 223
Cost Capitalized Subsequent to Initial Investment	246
Land	173
Building and Improvements	296
Total Investment in Real Estate	469
Accumulated Depreciation and Amortization	$ 141
Date of Initial Leasehold or Acquisition Investment	2000
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Astoria One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,684
Land	1,105
Building and Improvements	579
Total Investment in Real Estate	1,684
Accumulated Depreciation and Amortization	$ 188
Date of Initial Leasehold or Acquisition Investment	2013
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Avoca One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 936
Cost Capitalized Subsequent to Initial Investment	(1)
Land	635
Building and Improvements	300
Total Investment in Real Estate	935
Accumulated Depreciation and Amortization	$ 154
Date of Initial Leasehold or Acquisition Investment	2006
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Batavia One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 684
Land	364
Building and Improvements	320
Total Investment in Real Estate	684
Accumulated Depreciation and Amortization	$ 164
Date of Initial Leasehold or Acquisition Investment	2006
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Bay Shore One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 157
Cost Capitalized Subsequent to Initial Investment	355
Land	86
Building and Improvements	426
Total Investment in Real Estate	512
Accumulated Depreciation and Amortization	$ 286
Date of Initial Leasehold or Acquisition Investment	1981
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Bayside One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 470
Cost Capitalized Subsequent to Initial Investment	254
Land	306
Building and Improvements	418
Total Investment in Real Estate	724
Accumulated Depreciation and Amortization	$ 227
Date of Initial Leasehold or Acquisition Investment	1985