Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 6 (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
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Hartford Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	665
Land	432
Building and Improvements	233
Total Investment in Real Estate	665
Accumulated Depreciation and Amortization	$ 123
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | South Windham One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 644
Cost Capitalized Subsequent to Initial Investment	1,398
Land	598
Building and Improvements	1,444
Total Investment in Real Estate	2,042
Accumulated Depreciation and Amortization	$ 606
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Manchester One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 110
Cost Capitalized Subsequent to Initial Investment	323
Land	50
Building and Improvements	383
Total Investment in Real Estate	433
Accumulated Depreciation and Amortization	$ 176
Date of Initial Leasehold or Acquisition Investment	1987
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | South Windsor One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 545
Land	337
Building and Improvements	208
Total Investment in Real Estate	545
Accumulated Depreciation and Amortization	$ 122
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Meriden One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 208
Cost Capitalized Subsequent to Initial Investment	342
Land	84
Building and Improvements	466
Total Investment in Real Estate	550
Accumulated Depreciation and Amortization	$ 258
Date of Initial Leasehold or Acquisition Investment	1982
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Stamford One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 507
Cost Capitalized Subsequent to Initial Investment	16
Land	330
Building and Improvements	193
Total Investment in Real Estate	523
Accumulated Depreciation and Amortization	$ 157
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Meriden Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,532
Land	989
Building and Improvements	543
Total Investment in Real Estate	1,532
Accumulated Depreciation and Amortization	$ 290
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Stamford Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 604
Cost Capitalized Subsequent to Initial Investment	96
Land	393
Building and Improvements	307
Total Investment in Real Estate	700
Accumulated Depreciation and Amortization	$ 219
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Middletown One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 133
Cost Capitalized Subsequent to Initial Investment	550
Land	131
Building and Improvements	552
Total Investment in Real Estate	683
Accumulated Depreciation and Amortization	$ 288
Date of Initial Leasehold or Acquisition Investment	1987
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Stamford Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 507
Cost Capitalized Subsequent to Initial Investment	456
Land	330
Building and Improvements	633
Total Investment in Real Estate	963
Accumulated Depreciation and Amortization	$ 309
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Middletown Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,039
Land	675
Building and Improvements	364
Total Investment in Real Estate	1,039
Accumulated Depreciation and Amortization	$ 191
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Suffield 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	603
Land	201
Building and Improvements	639
Total Investment in Real Estate	840
Accumulated Depreciation and Amortization	$ 493
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Montville [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 57
Cost Capitalized Subsequent to Initial Investment	332
Land	24
Building and Improvements	365
Total Investment in Real Estate	389
Accumulated Depreciation and Amortization	$ 173
Date of Initial Leasehold or Acquisition Investment	1982
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Toll [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 108
Cost Capitalized Subsequent to Initial Investment	379
Land	44
Building and Improvements	443
Total Investment in Real Estate	487
Accumulated Depreciation and Amortization	$ 248
Date of Initial Leasehold or Acquisition Investment	1982
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | New Britain One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 391
Land	254
Building and Improvements	137
Total Investment in Real Estate	391
Accumulated Depreciation and Amortization	$ 72
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Vernon One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,434
Building and Improvements	1,434
Total Investment in Real Estate	1,434
Accumulated Depreciation and Amortization	$ 1,434
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | New Haven One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 217
Cost Capitalized Subsequent to Initial Investment	297
Land	141
Building and Improvements	373
Total Investment in Real Estate	514
Accumulated Depreciation and Amortization	$ 166
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Wallingford One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 551
Land	335
Building and Improvements	216
Total Investment in Real Estate	551
Accumulated Depreciation and Amortization	$ 130
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | New Haven Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 539
Cost Capitalized Subsequent to Initial Investment	454
Land	351
Building and Improvements	642
Total Investment in Real Estate	993
Accumulated Depreciation and Amortization	$ 408
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | New Haven Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,413
Cost Capitalized Subsequent to Initial Investment	(319)
Land	569
Building and Improvements	525
Total Investment in Real Estate	1,094
Accumulated Depreciation and Amortization	$ 154
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Newington One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 954
Land	620
Building and Improvements	334
Total Investment in Real Estate	954
Accumulated Depreciation and Amortization	$ 176
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | North Haven One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 405
Land	252
Building and Improvements	153
Total Investment in Real Estate	405
Accumulated Depreciation and Amortization	$ 89
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | North Haven Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 90
Cost Capitalized Subsequent to Initial Investment	669
Land	365
Building and Improvements	394
Total Investment in Real Estate	759
Accumulated Depreciation and Amortization	$ 175
Date of Initial Leasehold or Acquisition Investment	1982
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Norwalk One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 511
Cost Capitalized Subsequent to Initial Investment	47
Land	332
Building and Improvements	226
Total Investment in Real Estate	558
Accumulated Depreciation and Amortization	$ 188
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Norwalk Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Cost Capitalized Subsequent to Initial Investment	$ 941
Land	402
Building and Improvements	539
Total Investment in Real Estate	941
Accumulated Depreciation and Amortization	$ 232
Date of Initial Leasehold or Acquisition Investment	1988
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Norwich [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 107
Cost Capitalized Subsequent to Initial Investment	323
Land	44
Building and Improvements	386
Total Investment in Real Estate	430
Accumulated Depreciation and Amortization	$ 199
Date of Initial Leasehold or Acquisition Investment	1982
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Old Greenwich One [Member]
Schedule Of Investments In Real Estate [Line Items]
Cost Capitalized Subsequent to Initial Investment	$ 1,220
Land	620
Building and Improvements	600
Total Investment in Real Estate	1,220
Accumulated Depreciation and Amortization	$ 236
Date of Initial Leasehold or Acquisition Investment	1969
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Plainville One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 545
Land	354
Building and Improvements	191
Total Investment in Real Estate	545
Accumulated Depreciation and Amortization	$ 100
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Plymouth One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 931
Land	605
Building and Improvements	326
Total Investment in Real Estate	931
Accumulated Depreciation and Amortization	$ 172
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Ridgefield One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 402
Cost Capitalized Subsequent to Initial Investment	304
Land	167
Building and Improvements	539
Total Investment in Real Estate	706
Accumulated Depreciation and Amortization	$ 351
Date of Initial Leasehold or Acquisition Investment	1985