Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 14 (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
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	$ 226
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	$ 83
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	$ 362
Cost Capitalized Subsequent to Initial Investment	285
Land	200
Building and Improvements	447
Total Investment in Real Estate	647
Accumulated Depreciation and Amortization	$ 250
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	$ 382
Cost Capitalized Subsequent to Initial Investment	321
Land	300
Building and Improvements	403
Total Investment in Real Estate	703
Accumulated Depreciation and Amortization	$ 195
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	$ 470
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	(300)
Land	72
Building and Improvements	347
Total Investment in Real Estate	419
Accumulated Depreciation and Amortization	$ 273
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	$ 407
Cost Capitalized Subsequent to Initial Investment	29
Land	227
Building and Improvements	209
Total Investment in Real Estate	436
Accumulated Depreciation and Amortization	$ 170
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	$ 91
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	$ 177
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	362
Land	811
Building and Improvements	796
Total Investment in Real Estate	1,607
Accumulated Depreciation and Amortization	$ 488
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	$ 683
Cost Capitalized Subsequent to Initial Investment	173
Land	445
Building and Improvements	411
Total Investment in Real Estate	856
Accumulated Depreciation and Amortization	$ 329
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	$ 494
Cost Capitalized Subsequent to Initial Investment	198
Land	95
Building and Improvements	597
Total Investment in Real Estate	692
Accumulated Depreciation and Amortization	$ 82
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	$ 639
Cost Capitalized Subsequent to Initial Investment	393
Land	416
Building and Improvements	616
Total Investment in Real Estate	1,032
Accumulated Depreciation and Amortization	$ 397
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	$ 237
Cost Capitalized Subsequent to Initial Investment	186
Land	100
Building and Improvements	323
Total Investment in Real Estate	423
Accumulated Depreciation and Amortization	$ 222
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	$ 424
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	$ 353
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	426
Land	335
Building and Improvements	606
Total Investment in Real Estate	941
Accumulated Depreciation and Amortization	$ 275
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	418
Land	437
Building and Improvements	652
Total Investment in Real Estate	1,089
Accumulated Depreciation and Amortization	$ 291
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	311
Land	150
Building and Improvements	362
Total Investment in Real Estate	512
Accumulated Depreciation and Amortization	$ 185
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	$ 663
Cost Capitalized Subsequent to Initial Investment	(192)
Land	134
Building and Improvements	337
Total Investment in Real Estate	471
Accumulated Depreciation and Amortization	$ 118
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	148
Land	410
Building and Improvements	368
Total Investment in Real Estate	778
Accumulated Depreciation and Amortization	$ 281
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	$ 228
Cost Capitalized Subsequent to Initial Investment	553
Land	175
Building and Improvements	606
Total Investment in Real Estate	781
Accumulated Depreciation and Amortization	$ 417
Date of Initial Leasehold or Acquisition Investment	1978
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Nutley One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 434
Cost Capitalized Subsequent to Initial Investment	178
Land	283
Building and Improvements	329
Total Investment in Real Estate	612
Accumulated Depreciation and Amortization	$ 213
Date of Initial Leasehold or Acquisition Investment	1985
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	59
Land	249
Building and Improvements	192
Total Investment in Real Estate	441
Accumulated Depreciation and Amortization	$ 141
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Parlin One [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	153
Land	203
Building and Improvements	368
Total Investment in Real Estate	571
Accumulated Depreciation and Amortization	$ 121
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	$ 190
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Ridgewood One [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	393
Land	458
Building and Improvements	638
Total Investment in Real Estate	1,096
Accumulated Depreciation and Amortization	$ 350
Date of Initial Leasehold or Acquisition Investment	1985
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Somerville One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 253
Cost Capitalized Subsequent to Initial Investment	132
Land	201
Building and Improvements	184
Total Investment in Real Estate	385
Accumulated Depreciation and Amortization	$ 95
Date of Initial Leasehold or Acquisition Investment	1987
NJ [Member] | Accumulated Depreciation And Amortization Description [Member] | Trenton One [Member]
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	$ 48
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	$ 436
Cost Capitalized Subsequent to Initial Investment	209
Land	239
Building and Improvements	406
Total Investment in Real Estate	645
Accumulated Depreciation and Amortization	$ 151
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	277
Land	594
Building and Improvements	595
Total Investment in Real Estate	1,189
Accumulated Depreciation and Amortization	$ 355
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	$ 450
Cost Capitalized Subsequent to Initial Investment	115
Land	226
Building and Improvements	339
Total Investment in Real Estate	565
Accumulated Depreciation and Amortization	$ 106
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	$ 799
Cost Capitalized Subsequent to Initial Investment	397
Land	521
Building and Improvements	675
Total Investment in Real Estate	1,196
Accumulated Depreciation and Amortization	$ 428
Date of Initial Leasehold or Acquisition Investment	1985
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	$ 142
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	$ 116
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	$ 155
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	$ 142
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	$ 151
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	$ 263
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	$ 199
Date of Initial Leasehold or Acquisition Investment	1985
NEW MEXICO [Member] | Accumulated Depreciation And Amortization Description [Member] | Albuquerque 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	$ 9
Date of Initial Leasehold or Acquisition Investment	2017
NEW MEXICO [Member] | Accumulated Depreciation And Amortization Description [Member] | Albuquerque 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	$ 11
Date of Initial Leasehold or Acquisition Investment	2017
NEW MEXICO [Member] | Accumulated Depreciation And Amortization Description [Member] | Albuquerque 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	$ 11
Date of Initial Leasehold or Acquisition Investment	2017
NEW MEXICO [Member] | Accumulated Depreciation And Amortization Description [Member] | Albuquerque 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	$ 12
Date of Initial Leasehold or Acquisition Investment	2017
NEW MEXICO [Member] | Accumulated Depreciation And Amortization Description [Member] | Las Cruces One
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	$ 10
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	$ 264
Date of Initial Leasehold or Acquisition Investment	2015