Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 10 (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 YORK | Niskayuna One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	425
Cost Capitalized Subsequent to Initial Investment	35
Land	275
Building and Improvements	185
Total Investment in Real Estate	460
Accumulated Depreciation and Amortization	$ 185
Date of Initial Leasehold or Acquisition Investment	1986
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Ossining One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 231
Cost Capitalized Subsequent to Initial Investment	197
Land	117
Building and Improvements	311
Total Investment in Real Estate	428
Accumulated Depreciation and Amortization	$ 202
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Peekskill One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,207
Land	2,207
Total Investment in Real Estate	$ 2,207
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Pelham One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 137
Cost Capitalized Subsequent to Initial Investment	307
Land	75
Building and Improvements	369
Total Investment in Real Estate	444
Accumulated Depreciation and Amortization	$ 253
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Pelham Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,035
Land	1,035
Total Investment in Real Estate	$ 1,035
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Perry [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,444
Land	1,044
Building and Improvements	400
Total Investment in Real Estate	1,444
Accumulated Depreciation and Amortization	$ 221
Date of Initial Leasehold or Acquisition Investment	2006
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Pleasant Valley One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 398
Cost Capitalized Subsequent to Initial Investment	183
Land	240
Building and Improvements	341
Total Investment in Real Estate	581
Accumulated Depreciation and Amortization	$ 217
Date of Initial Leasehold or Acquisition Investment	1986
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Port Chester One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,015
Land	1,015
Total Investment in Real Estate	$ 1,015
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Port Jefferson One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 185
Cost Capitalized Subsequent to Initial Investment	3,084
Land	246
Building and Improvements	3,023
Total Investment in Real Estate	3,269
Accumulated Depreciation and Amortization	$ 189
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Poughkeepsie One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 591
Land	591
Total Investment in Real Estate	$ 591
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Poughkeepsie Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,020
Land	1,020
Total Investment in Real Estate	$ 1,020
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Poughkeepsie Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,340
Cost Capitalized Subsequent to Initial Investment	(60)
Land	1,280
Total Investment in Real Estate	$ 1,280
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Poughkeepsie Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,306
Land	1,306
Total Investment in Real Estate	$ 1,306
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Poughkeepsie Five [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,355
Land	1,355
Total Investment in Real Estate	$ 1,355
Date of Initial Leasehold or Acquisition Investment	2011
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Poughkeepsie Six [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,232
Cost Capitalized Subsequent to Initial Investment	(32)
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 YORK | Prattsburgh One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 553
Land	303
Building and Improvements	250
Total Investment in Real Estate	553
Accumulated Depreciation and Amortization	$ 138
Date of Initial Leasehold or Acquisition Investment	2006
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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	$ 250
Date of Initial Leasehold or Acquisition Investment	2013
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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	$ 253
Date of Initial Leasehold or Acquisition Investment	1998
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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	$ 251
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Saint 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	$ 191
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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	$ 161
Date of Initial Leasehold or Acquisition Investment	1998
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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	398
Land	691
Building and Improvements	768
Total Investment in Real Estate	1,459
Accumulated Depreciation and Amortization	$ 558
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Sleepy Hollow One [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	316
Land	130
Building and Improvements	468
Total Investment in Real Estate	598
Accumulated Depreciation and Amortization	$ 414
Date of Initial Leasehold or Acquisition Investment	1969
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Staten Island One [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	$ 292
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Staten Island Two [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	$ 274
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Staten Island Three [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	$ 208
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Staten Island Four [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	$ 234
Date of Initial Leasehold or Acquisition Investment	1978
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Tuckahoe 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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Wantagh One [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	$ 230
Date of Initial Leasehold or Acquisition Investment	1998
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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	$ 166
Date of Initial Leasehold or Acquisition Investment	2006
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | 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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | West Nyack One [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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | White Plains One [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	$ 213
Date of Initial Leasehold or Acquisition Investment	1972
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | White Plains Two [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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Yaphank One [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	$ 221
Date of Initial Leasehold or Acquisition Investment	1993
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Yonkers One [Members]
Schedule Of Investments In Real Estate [Line Items]
Cost Capitalized Subsequent to Initial Investment	$ 543
Building and Improvements	543
Total Investment in Real Estate	543
Accumulated Depreciation and Amortization	$ 388
Date of Initial Leasehold or Acquisition Investment	1970
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Yonkers Two [Members]
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	$ 631
Date of Initial Leasehold or Acquisition Investment	1972
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Yonkers Three [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	$ 131
Date of Initial Leasehold or Acquisition Investment	1990
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Yonkers Four [Members]
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	$ 375
Date of Initial Leasehold or Acquisition Investment	1985
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Yonkers Five [Members]
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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Yorktown Heights One [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
Accumulated Depreciation And Amortization Description [Member] | NEW YORK | Yorktown Heights Two [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	$ 387
Date of Initial Leasehold or Acquisition Investment	2013