Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 6 (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
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Waterbury One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	469
Land	305
Building and Improvements	164
Total Investment in Real Estate	469
Accumulated Depreciation and Amortization	$ 93
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Waterbury Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 515
Land	335
Building and Improvements	180
Total Investment in Real Estate	515
Accumulated Depreciation and Amortization	$ 102
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Waterbury Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 804
Land	516
Building and Improvements	288
Total Investment in Real Estate	804
Accumulated Depreciation and Amortization	$ 167
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Watertown Five [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 352
Cost Capitalized Subsequent to Initial Investment	59
Land	204
Building and Improvements	207
Total Investment in Real Estate	411
Accumulated Depreciation and Amortization	$ 168
Date of Initial Leasehold or Acquisition Investment	1992
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Watertown Six [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 925
Land	567
Building and Improvements	358
Total Investment in Real Estate	925
Accumulated Depreciation and Amortization	$ 225
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | West Haven 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	322
Land	74
Building and Improvements	433
Total Investment in Real Estate	507
Accumulated Depreciation and Amortization	$ 269
Date of Initial Leasehold or Acquisition Investment	1982
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | West Haven Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,215
Land	790
Building and Improvements	425
Total Investment in Real Estate	1,215
Accumulated Depreciation and Amortization	$ 241
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Westport One [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	12
Land	393
Building and Improvements	223
Total Investment in Real Estate	616
Accumulated Depreciation and Amortization	$ 189
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Wethersfield One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 447
Building and Improvements	447
Total Investment in Real Estate	447
Accumulated Depreciation and Amortization	$ 447
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Willimantic One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 717
Land	466
Building and Improvements	251
Total Investment in Real Estate	717
Accumulated Depreciation and Amortization	$ 142
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Wilton One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 519
Cost Capitalized Subsequent to Initial Investment	214
Land	338
Building and Improvements	395
Total Investment in Real Estate	733
Accumulated Depreciation and Amortization	$ 295
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Windsor Locks One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,031
Land	670
Building and Improvements	361
Total Investment in Real Estate	1,031
Accumulated Depreciation and Amortization	$ 204
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Windsor Locks Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,434
Cost Capitalized Subsequent to Initial Investment	1,400
Land	1,055
Building and Improvements	1,779
Total Investment in Real Estate	2,834
Accumulated Depreciation and Amortization	$ 1,484
Date of Initial Leasehold or Acquisition Investment	2004
DISTRICT OF COLUMBIA [Member] | Accumulated Depreciation And Amortization Description [Member] | Washington One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 848
Land	418
Building and Improvements	430
Total Investment in Real Estate	848
Accumulated Depreciation and Amortization	$ 121
Date of Initial Leasehold or Acquisition Investment	2013
DISTRICT OF COLUMBIA [Member] | Accumulated Depreciation And Amortization Description [Member] | Washington Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 941
Land	664
Building and Improvements	277
Total Investment in Real Estate	941
Accumulated Depreciation and Amortization	$ 90
Date of Initial Leasehold or Acquisition Investment	2013
FLORIDA [Member] | Accumulated Depreciation And Amortization Description [Member] | Nassau One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,963
Land	570
Building and Improvements	1,393
Total Investment in Real Estate	1,963
Accumulated Depreciation and Amortization	$ 102
Date of Initial Leasehold or Acquisition Investment	2017
FLORIDA [Member] | Accumulated Depreciation And Amortization Description [Member] | Nassau Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,137
Land	382
Building and Improvements	1,755
Total Investment in Real Estate	2,137
Accumulated Depreciation and Amortization	$ 129
Date of Initial Leasehold or Acquisition Investment	2017