Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 7 (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] | NEW HAMPSHIRE [Member] | Derry [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	950
Land	950
Building and Improvements	0
Total Investment in Real Estate	950
Accumulated Depreciation and Amortization	$ 0
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Derry One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 650
Land	650
Total Investment in Real Estate	$ 650
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Dover Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,200
Land	1,200
Total Investment in Real Estate	$ 1,200
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Goffstown One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,737
Land	697
Building and Improvements	1,040
Total Investment in Real Estate	1,737
Accumulated Depreciation and Amortization	$ 522
Date of Initial Leasehold or Acquisition Investment	2012
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Hooksett One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,562
Land	824
Building and Improvements	738
Total Investment in Real Estate	1,562
Accumulated Depreciation and Amortization	$ 676
Date of Initial Leasehold or Acquisition Investment	2007
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Kingston One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,500
Land	1,500
Total Investment in Real Estate	$ 1,500
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Londonderry 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	30
Land	458
Building and Improvements	275
Total Investment in Real Estate	733
Accumulated Depreciation and Amortization	$ 245
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Londonderry Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,100
Land	1,100
Total Investment in Real Estate	$ 1,100
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Manchester One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 550
Land	550
Total Investment in Real Estate	$ 550
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Nashua One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 825
Land	825
Total Investment in Real Estate	$ 825
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Nashua Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 750
Land	750
Total Investment in Real Estate	$ 750
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Nashua Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,750
Land	1,750
Total Investment in Real Estate	$ 1,750
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Nashua Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 500
Land	500
Total Investment in Real Estate	$ 500
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Nashua Five [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 550
Land	550
Total Investment in Real Estate	$ 550
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Nashua Six [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,132
Land	780
Building and Improvements	352
Total Investment in Real Estate	1,132
Accumulated Depreciation and Amortization	$ 56
Date of Initial Leasehold or Acquisition Investment	2017
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Northwood One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 500
Land	500
Total Investment in Real Estate	$ 500
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Pelham One [Member]
Schedule Of Investments In Real Estate [Line Items]
Cost Capitalized Subsequent to Initial Investment	$ 730
Land	317
Building and Improvements	413
Total Investment in Real Estate	730
Accumulated Depreciation and Amortization	$ 146
Date of Initial Leasehold or Acquisition Investment	1996
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Portsmouth One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 525
Land	525
Total Investment in Real Estate	$ 525
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Raymond One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 550
Land	550
Total Investment in Real Estate	$ 550
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Rochester One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 939
Cost Capitalized Subsequent to Initial Investment	12
Land	600
Building and Improvements	351
Total Investment in Real Estate	951
Accumulated Depreciation and Amortization	$ 310
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Rochester Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,400
Land	1,400
Total Investment in Real Estate	$ 1,400
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Rochester Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,600
Land	1,600
Total Investment in Real Estate	$ 1,600
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [Member] | Rochester Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 700
Land	700
Total Investment in Real Estate	$ 700
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [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	$ 247
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW HAMPSHIRE [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	$ 161
Date of Initial Leasehold or Acquisition Investment	1986
Accumulated Depreciation And Amortization Description [Member] | NJ [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	$ 306
Date of Initial Leasehold or Acquisition Investment	1986
Accumulated Depreciation And Amortization Description [Member] | NJ [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	322
Land	300
Building and Improvements	404
Total Investment in Real Estate	704
Accumulated Depreciation and Amortization	$ 255
Date of Initial Leasehold or Acquisition Investment	1990
Accumulated Depreciation And Amortization Description [Member] | NJ [Member] | Brick One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,507
Cost Capitalized Subsequent to Initial Investment	246
Land	1,000
Building and Improvements	753
Total Investment in Real Estate	1,753
Accumulated Depreciation and Amortization	$ 548
Date of Initial Leasehold or Acquisition Investment	2000
Accumulated Depreciation And Amortization Description [Member] | NJ [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	(284)
Land	72
Building and Improvements	363
Total Investment in Real Estate	435
Accumulated Depreciation and Amortization	$ 292
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [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	29
Land	227
Building and Improvements	208
Total Investment in Real Estate	435
Accumulated Depreciation and Amortization	$ 195
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [Member] | Flemington One [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	$ 193
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [Member] | Flemington Two [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	$ 150
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [Member] | FortLee One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,246
Cost Capitalized Subsequent to Initial Investment	383
Land	811
Building and Improvements	818
Total Investment in Real Estate	1,629
Accumulated Depreciation and Amortization	$ 588
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [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	683
Land	95
Building and Improvements	1,082
Total Investment in Real Estate	1,177
Accumulated Depreciation and Amortization	$ 265
Date of Initial Leasehold or Acquisition Investment	1978
Accumulated Depreciation And Amortization Description [Member] | NJ [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	538
Land	416
Building and Improvements	762
Total Investment in Real Estate	1,178
Accumulated Depreciation and Amortization	$ 509
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [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	$ 268
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [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	$ 449
Date of Initial Leasehold or Acquisition Investment	2000
Accumulated Depreciation And Amortization Description [Member] | NJ [Member] | Lawrence Township 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	$ 68
Date of Initial Leasehold or Acquisition Investment	2012
Accumulated Depreciation And Amortization Description [Member] | NJ [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	54
Land	568
Building and Improvements	358
Total Investment in Real Estate	926
Accumulated Depreciation and Amortization	$ 306
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [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	494
Land	335
Building and Improvements	674
Total Investment in Real Estate	1,009
Accumulated Depreciation and Amortization	$ 374
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [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	$ 233
Date of Initial Leasehold or Acquisition Investment	1989
Accumulated Depreciation And Amortization Description [Member] | NJ [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	(189)
Land	134
Building and Improvements	341
Total Investment in Real Estate	475
Accumulated Depreciation and Amortization	$ 186
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [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	$ 312
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [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	543
Land	175
Building and Improvements	595
Total Investment in Real Estate	770
Accumulated Depreciation and Amortization	$ 478
Date of Initial Leasehold or Acquisition Investment	1978
Accumulated Depreciation And Amortization Description [Member] | NJ [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	86
Land	249
Building and Improvements	219
Total Investment in Real Estate	468
Accumulated Depreciation and Amortization	$ 162
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [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	161
Land	203
Building and Improvements	376
Total Investment in Real Estate	579
Accumulated Depreciation and Amortization	$ 196
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [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	$ 207
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NJ [Member] | Ridgewood One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 704
Cost Capitalized Subsequent to Initial Investment	423
Land	458
Building and Improvements	669
Total Investment in Real Estate	1,127
Accumulated Depreciation and Amortization	$ 443
Date of Initial Leasehold or Acquisition Investment	1985