Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 17 (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 YORK | Accumulated Depreciation And Amortization Description [Member] | Rego Park One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	2,783
Land	2,104
Building and Improvements	679
Total Investment in Real Estate	2,783
Accumulated Depreciation and Amortization	$ 213
Date of Initial Leasehold or Acquisition Investment	2013
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Riverhead One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 724
Land	432
Building and Improvements	292
Total Investment in Real Estate	724
Accumulated Depreciation and Amortization	$ 241
Date of Initial Leasehold or Acquisition Investment	1998
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Rockaway Park One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,605
Land	1,605
Total Investment in Real Estate	$ 1,605
Date of Initial Leasehold or Acquisition Investment	2013
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Rockville Centre One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 350
Cost Capitalized Subsequent to Initial Investment	66
Land	201
Building and Improvements	215
Total Investment in Real Estate	416
Accumulated Depreciation and Amortization	$ 197
Date of Initial Leasehold or Acquisition Investment	1985
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Rye One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 872
Land	872
Total Investment in Real Estate	$ 872
Date of Initial Leasehold or Acquisition Investment	2011
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Sag Harbor 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	35
Land	458
Building and Improvements	281
Total Investment in Real Estate	739
Accumulated Depreciation and Amortization	$ 241
Date of Initial Leasehold or Acquisition Investment	1985
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Sayville One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 344
Cost Capitalized Subsequent to Initial Investment	246
Land	300
Building and Improvements	290
Total Investment in Real Estate	590
Accumulated Depreciation and Amortization	$ 134
Date of Initial Leasehold or Acquisition Investment	1998
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Scarsdale One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,301
Land	1,301
Total Investment in Real Estate	$ 1,301
Date of Initial Leasehold or Acquisition Investment	2011
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Shrub Oak One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,061
Cost Capitalized Subsequent to Initial Investment	368
Land	691
Building and Improvements	738
Total Investment in Real Estate	1,429
Accumulated Depreciation and Amortization	$ 511
Date of Initial Leasehold or Acquisition Investment	1985
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Sleepy Hollow One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 281
Cost Capitalized Subsequent to Initial Investment	301
Land	130
Building and Improvements	452
Total Investment in Real Estate	582
Accumulated Depreciation and Amortization	$ 392
Date of Initial Leasehold or Acquisition Investment	1969
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Spring Valley One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 749
Land	749
Total Investment in Real Estate	$ 749
Date of Initial Leasehold or Acquisition Investment	2011
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | St Albans One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 330
Cost Capitalized Subsequent to Initial Investment	106
Land	215
Building and Improvements	221
Total Investment in Real Estate	436
Accumulated Depreciation and Amortization	$ 183
Date of Initial Leasehold or Acquisition Investment	1985
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Staten Island One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 390
Cost Capitalized Subsequent to Initial Investment	89
Land	254
Building and Improvements	225
Total Investment in Real Estate	479
Accumulated Depreciation and Amortization	$ 203
Date of Initial Leasehold or Acquisition Investment	1985
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Staten Island Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 301
Cost Capitalized Subsequent to Initial Investment	323
Land	196
Building and Improvements	428
Total Investment in Real Estate	624
Accumulated Depreciation and Amortization	$ 263
Date of Initial Leasehold or Acquisition Investment	1985
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Staten Island Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 350
Cost Capitalized Subsequent to Initial Investment	290
Land	228
Building and Improvements	412
Total Investment in Real Estate	640
Accumulated Depreciation and Amortization	$ 244
Date of Initial Leasehold or Acquisition Investment	1985
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Stony Brook One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 176
Cost Capitalized Subsequent to Initial Investment	281
Land	105
Building and Improvements	352
Total Investment in Real Estate	457
Accumulated Depreciation and Amortization	$ 210
Date of Initial Leasehold or Acquisition Investment	1978
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Tarrytown One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 956
Land	956
Total Investment in Real Estate	$ 956
Date of Initial Leasehold or Acquisition Investment	2011
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Tuchahoe One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,650
Land	1,650
Total Investment in Real Estate	$ 1,650
Date of Initial Leasehold or Acquisition Investment	2011
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Wantagh [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 640
Land	370
Building and Improvements	270
Total Investment in Real Estate	640
Accumulated Depreciation and Amortization	$ 219
Date of Initial Leasehold or Acquisition Investment	1998
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Wappingers Falls Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 452
Building and Improvements	452
Total Investment in Real Estate	452
Accumulated Depreciation and Amortization	$ 323
Date of Initial Leasehold or Acquisition Investment	2011
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Wappingers Falls One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,488
Land	1,488
Total Investment in Real Estate	$ 1,488
Date of Initial Leasehold or Acquisition Investment	2011
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Warsaw One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 990
Land	690
Building and Improvements	300
Total Investment in Real Estate	990
Accumulated Depreciation and Amortization	$ 154
Date of Initial Leasehold or Acquisition Investment	2006
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Warwick One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,049
Land	1,049
Total Investment in Real Estate	$ 1,049
Date of Initial Leasehold or Acquisition Investment	2011
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | West Nyack [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 936
Land	936
Total Investment in Real Estate	$ 936
Date of Initial Leasehold or Acquisition Investment	2011
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | White Plains [Member]
Schedule Of Investments In Real Estate [Line Items]
Cost Capitalized Subsequent to Initial Investment	$ 569
Land	303
Building and Improvements	266
Total Investment in Real Estate	569
Accumulated Depreciation and Amortization	$ 204
Date of Initial Leasehold or Acquisition Investment	1972
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | White Plains One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,458
Land	1,458
Total Investment in Real Estate	$ 1,458
Date of Initial Leasehold or Acquisition Investment	2011
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Yaphank [Member]
Schedule Of Investments In Real Estate [Line Items]
Cost Capitalized Subsequent to Initial Investment	$ 798
Land	375
Building and Improvements	423
Total Investment in Real Estate	798
Accumulated Depreciation and Amortization	$ 182
Date of Initial Leasehold or Acquisition Investment	1993
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Yonkers One [Member]
Schedule Of Investments In Real Estate [Line Items]
Cost Capitalized Subsequent to Initial Investment	$ 588
Building and Improvements	588
Total Investment in Real Estate	588
Accumulated Depreciation and Amortization	$ 345
Date of Initial Leasehold or Acquisition Investment	1970
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Yonkers Two [Members]
Schedule Of Investments In Real Estate [Line Items]
Cost Capitalized Subsequent to Initial Investment	$ 944
Land	684
Building and Improvements	260
Total Investment in Real Estate	944
Accumulated Depreciation and Amortization	$ 114
Date of Initial Leasehold or Acquisition Investment	1990
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Yonkers Five [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,021
Cost Capitalized Subsequent to Initial Investment	63
Land	665
Building and Improvements	419
Total Investment in Real Estate	1,084
Accumulated Depreciation and Amortization	$ 361
Date of Initial Leasehold or Acquisition Investment	1985
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Yonkers Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 291
Cost Capitalized Subsequent to Initial Investment	1,050
Land	216
Building and Improvements	1,125
Total Investment in Real Estate	1,341
Accumulated Depreciation and Amortization	$ 542
Date of Initial Leasehold or Acquisition Investment	1972
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Yonkers Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,907
Land	1,907
Total Investment in Real Estate	$ 1,907
Date of Initial Leasehold or Acquisition Investment	2011
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Yorktown Heights One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,700
Building and Improvements	1,700
Total Investment in Real Estate	1,700
Accumulated Depreciation and Amortization	$ 274
Date of Initial Leasehold or Acquisition Investment	2013
NEW YORK | Accumulated Depreciation And Amortization Description [Member] | Yorktown Heights Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,365
Land	2,365
Total Investment in Real Estate	$ 2,365
Date of Initial Leasehold or Acquisition Investment	2011
OHIO | Accumulated Depreciation And Amortization Description [Member] | Clermont [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,045
Land	362
Building and Improvements	683
Total Investment in Real Estate	1,045
Accumulated Depreciation and Amortization	$ 64
Date of Initial Leasehold or Acquisition Investment	2017
OHIO | Accumulated Depreciation And Amortization Description [Member] | Crestline One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,202
Land	285
Building and Improvements	917
Total Investment in Real Estate	1,202
Accumulated Depreciation and Amortization	$ 463
Date of Initial Leasehold or Acquisition Investment	2008
OHIO | Accumulated Depreciation And Amortization Description [Member] | Mansfield One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 922
Land	332
Building and Improvements	590
Total Investment in Real Estate	922
Accumulated Depreciation and Amortization	$ 280
Date of Initial Leasehold or Acquisition Investment	2008
OHIO | Accumulated Depreciation And Amortization Description [Member] | Mansfield Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,950
Land	700
Building and Improvements	1,250
Total Investment in Real Estate	1,950
Accumulated Depreciation and Amortization	$ 587
Date of Initial Leasehold or Acquisition Investment	2009
OHIO | Accumulated Depreciation And Amortization Description [Member] | Monroeville One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,580
Land	485
Building and Improvements	2,095
Total Investment in Real Estate	2,580
Accumulated Depreciation and Amortization	$ 970
Date of Initial Leasehold or Acquisition Investment	2009
OHIO | Accumulated Depreciation And Amortization Description [Member] | Summit [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,530
Land	385
Building and Improvements	1,145
Total Investment in Real Estate	1,530
Accumulated Depreciation and Amortization	$ 95
Date of Initial Leasehold or Acquisition Investment	2017
OKLAHOMA | Accumulated Depreciation And Amortization Description [Member] | Oklahoma City One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 868
Land	371
Building and Improvements	497
Total Investment in Real Estate	868
Accumulated Depreciation and Amortization	$ 19
Date of Initial Leasehold or Acquisition Investment	2018
OKLAHOMA | Accumulated Depreciation And Amortization Description [Member] | Oklahoma City Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,182
Land	587
Building and Improvements	595
Total Investment in Real Estate	1,182
Accumulated Depreciation and Amortization	$ 22
Date of Initial Leasehold or Acquisition Investment	2018
OKLAHOMA | Accumulated Depreciation And Amortization Description [Member] | Oklahoma City Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,311
Land	625
Building and Improvements	686
Total Investment in Real Estate	1,311
Accumulated Depreciation and Amortization	$ 24
Date of Initial Leasehold or Acquisition Investment	2018
OREGON | Accumulated Depreciation And Amortization Description [Member] | Banks One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 498
Land	498
Total Investment in Real Estate	$ 498
Date of Initial Leasehold or Acquisition Investment	2015
OREGON | Accumulated Depreciation And Amortization Description [Member] | Estacada One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 646
Land	84
Building and Improvements	562
Total Investment in Real Estate	646
Accumulated Depreciation and Amortization	$ 109
Date of Initial Leasehold or Acquisition Investment	2015
OREGON | Accumulated Depreciation And Amortization Description [Member] | Marion One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 543
Land	296
Building and Improvements	247
Total Investment in Real Estate	543
Accumulated Depreciation and Amortization	$ 29
Date of Initial Leasehold or Acquisition Investment	2017
OREGON | Accumulated Depreciation And Amortization Description [Member] | Marion Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 956
Land	456
Building and Improvements	500
Total Investment in Real Estate	956
Accumulated Depreciation and Amortization	$ 50
Date of Initial Leasehold or Acquisition Investment	2017
OREGON | Accumulated Depreciation And Amortization Description [Member] | Pendleton One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 766
Land	122
Building and Improvements	644
Total Investment in Real Estate	766
Accumulated Depreciation and Amortization	$ 138
Date of Initial Leasehold or Acquisition Investment	2015
OREGON | Accumulated Depreciation And Amortization Description [Member] | Portland One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 4,416
Land	3,368
Building and Improvements	1,048
Total Investment in Real Estate	4,416
Accumulated Depreciation and Amortization	$ 213
Date of Initial Leasehold or Acquisition Investment	2015