Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 15 (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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Brewster One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	789
Land	789
Total Investment in Real Estate	$ 789
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Briarcliff Manor One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 652
Cost Capitalized Subsequent to Initial Investment	553
Land	502
Building and Improvements	703
Total Investment in Real Estate	1,205
Accumulated Depreciation and Amortization	$ 515
Date of Initial Leasehold or Acquisition Investment	1976
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Bronx One
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 423
Land	423
Total Investment in Real Estate	$ 423
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Bronx Two [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	54
Land	251
Building and Improvements	193
Total Investment in Real Estate	444
Accumulated Depreciation and Amortization	$ 171
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Bronx Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 877
Land	877
Total Investment in Real Estate	$ 877
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Bronx Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 884
Land	884
Total Investment in Real Estate	$ 884
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Bronx Five [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 953
Land	953
Total Investment in Real Estate	$ 953
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Bronx Six [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,049
Land	485
Building and Improvements	564
Total Investment in Real Estate	1,049
Accumulated Depreciation and Amortization	$ 184
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Bronx Seven [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,910
Land	1,349
Building and Improvements	561
Total Investment in Real Estate	1,910
Accumulated Depreciation and Amortization	$ 191
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Bronx Eight [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,408
Land	1,712
Building and Improvements	696
Total Investment in Real Estate	2,408
Accumulated Depreciation and Amortization	$ 214
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Bronxville [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,232
Land	1,232
Total Investment in Real Estate	$ 1,232
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Brooklyn One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 100
Cost Capitalized Subsequent to Initial Investment	345
Land	67
Building and Improvements	378
Total Investment in Real Estate	445
Accumulated Depreciation and Amortization	$ 227
Date of Initial Leasehold or Acquisition Investment	1972
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Brooklyn Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 75
Cost Capitalized Subsequent to Initial Investment	382
Land	31
Building and Improvements	426
Total Investment in Real Estate	457
Accumulated Depreciation and Amortization	$ 264
Date of Initial Leasehold or Acquisition Investment	1967
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Brooklyn Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 282
Cost Capitalized Subsequent to Initial Investment	271
Land	176
Building and Improvements	377
Total Investment in Real Estate	553
Accumulated Depreciation and Amortization	$ 361
Date of Initial Leasehold or Acquisition Investment	1967
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Brooklyn Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 148
Cost Capitalized Subsequent to Initial Investment	437
Land	104
Building and Improvements	481
Total Investment in Real Estate	585
Accumulated Depreciation and Amortization	$ 294
Date of Initial Leasehold or Acquisition Investment	1972
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Brooklyn Five [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	372
Land	154
Building and Improvements	455
Total Investment in Real Estate	609
Accumulated Depreciation and Amortization	$ 233
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Brooklyn Six
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 476
Cost Capitalized Subsequent to Initial Investment	320
Land	306
Building and Improvements	490
Total Investment in Real Estate	796
Accumulated Depreciation and Amortization	$ 316
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Brooklyn Seven [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 422
Cost Capitalized Subsequent to Initial Investment	383
Land	275
Building and Improvements	530
Total Investment in Real Estate	805
Accumulated Depreciation and Amortization	$ 322
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Brooklyn Eight [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 627
Cost Capitalized Subsequent to Initial Investment	313
Land	408
Building and Improvements	532
Total Investment in Real Estate	940
Accumulated Depreciation and Amortization	$ 342
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Buffalo [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 313
Cost Capitalized Subsequent to Initial Investment	241
Land	151
Building and Improvements	403
Total Investment in Real Estate	554
Accumulated Depreciation and Amortization	$ 228
Date of Initial Leasehold or Acquisition Investment	2000
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Byron [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 969
Land	669
Building and Improvements	300
Total Investment in Real Estate	969
Accumulated Depreciation and Amortization	$ 154
Date of Initial Leasehold or Acquisition Investment	2006
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Chester [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,158
Land	1,158
Total Investment in Real Estate	$ 1,158
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Churchville [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,012
Land	602
Building and Improvements	410
Total Investment in Real Estate	1,012
Accumulated Depreciation and Amortization	$ 210
Date of Initial Leasehold or Acquisition Investment	2006
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Corona One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 115
Cost Capitalized Subsequent to Initial Investment	300
Land	113
Building and Improvements	302
Total Investment in Real Estate	415
Accumulated Depreciation and Amortization	$ 302
Date of Initial Leasehold or Acquisition Investment	1965
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Corona Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,543
Land	1,903
Building and Improvements	640
Total Investment in Real Estate	2,543
Accumulated Depreciation and Amortization	$ 200
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Cortland Manor [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,872
Land	1,872
Total Investment in Real Estate	$ 1,872
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Dobbs Ferry One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 670
Cost Capitalized Subsequent to Initial Investment	34
Land	434
Building and Improvements	270
Total Investment in Real Estate	704
Accumulated Depreciation and Amortization	$ 232
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Dobbs Ferry Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,345
Land	1,345
Total Investment in Real Estate	$ 1,345
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | East Hampton One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 660
Cost Capitalized Subsequent to Initial Investment	39
Land	428
Building and Improvements	271
Total Investment in Real Estate	699
Accumulated Depreciation and Amortization	$ 233
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Eastchester One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,724
Cost Capitalized Subsequent to Initial Investment	993
Land	2,302
Building and Improvements	415
Total Investment in Real Estate	2,717
Accumulated Depreciation and Amortization	$ 45
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Elmont One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 389
Cost Capitalized Subsequent to Initial Investment	319
Land	231
Building and Improvements	477
Total Investment in Real Estate	708
Accumulated Depreciation and Amortization	$ 333
Date of Initial Leasehold or Acquisition Investment	1978
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Elmsford One [Member]
Schedule Of Investments In Real Estate [Line Items]
Cost Capitalized Subsequent to Initial Investment	$ 948
Land	581
Building and Improvements	367
Total Investment in Real Estate	948
Accumulated Depreciation and Amortization	$ 244
Date of Initial Leasehold or Acquisition Investment	1971
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Elmsford Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,453
Land	1,453
Total Investment in Real Estate	$ 1,453
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Fishkill One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,793
Land	1,793
Total Investment in Real Estate	$ 1,793
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Floral Park One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 616
Cost Capitalized Subsequent to Initial Investment	170
Land	356
Building and Improvements	430
Total Investment in Real Estate	786
Accumulated Depreciation and Amortization	$ 275
Date of Initial Leasehold or Acquisition Investment	1998
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Flushing One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 516
Cost Capitalized Subsequent to Initial Investment	241
Land	320
Building and Improvements	437
Total Investment in Real Estate	757
Accumulated Depreciation and Amortization	$ 258
Date of Initial Leasehold or Acquisition Investment	1998
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Flushing Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,936
Land	1,413
Building and Improvements	523
Total Investment in Real Estate	1,936
Accumulated Depreciation and Amortization	$ 170
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Flushing Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,947
Land	1,405
Building and Improvements	542
Total Investment in Real Estate	1,947
Accumulated Depreciation and Amortization	$ 162
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Flushing Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,478
Land	1,801
Building and Improvements	677
Total Investment in Real Estate	2,478
Accumulated Depreciation and Amortization	$ 203
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Forrest Hill One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,273
Land	1,273
Total Investment in Real Estate	$ 1,273
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Franklin Square One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 153
Cost Capitalized Subsequent to Initial Investment	331
Land	137
Building and Improvements	347
Total Investment in Real Estate	484
Accumulated Depreciation and Amortization	$ 195
Date of Initial Leasehold or Acquisition Investment	1978
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | East Pembroke One
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 787
Land	537
Building and Improvements	250
Total Investment in Real Estate	787
Accumulated Depreciation and Amortization	$ 128
Date of Initial Leasehold or Acquisition Investment	2006