Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 4 (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] | Bridgeport 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	330
Land	228
Building and Improvements	452
Total Investment in Real Estate	680
Accumulated Depreciation and Amortization	$ 235
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Bridgeport Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 378
Cost Capitalized Subsequent to Initial Investment	391
Land	246
Building and Improvements	523
Total Investment in Real Estate	769
Accumulated Depreciation and Amortization	$ 290
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Bristol Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,594
Land	1,036
Building and Improvements	558
Total Investment in Real Estate	1,594
Accumulated Depreciation and Amortization	$ 294
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Brookfield One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 58
Cost Capitalized Subsequent to Initial Investment	683
Land	20
Building and Improvements	721
Total Investment in Real Estate	741
Accumulated Depreciation and Amortization	$ 352
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Darien One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 667
Cost Capitalized Subsequent to Initial Investment	295
Land	434
Building and Improvements	528
Total Investment in Real Estate	962
Accumulated Depreciation and Amortization	$ 388
Date of Initial Leasehold or Acquisition Investment	1985
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Durham One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 994
Building and Improvements	994
Total Investment in Real Estate	994
Accumulated Depreciation and Amortization	$ 994
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | East Hartford 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	224
Land	54
Building and Improvements	378
Total Investment in Real Estate	432
Accumulated Depreciation and Amortization	$ 243
Date of Initial Leasehold or Acquisition Investment	1982
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Ellington One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,295
Land	842
Building and Improvements	453
Total Investment in Real Estate	1,295
Accumulated Depreciation and Amortization	$ 239
Date of Initial Leasehold or Acquisition Investment	2004
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Fairfield One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 430
Cost Capitalized Subsequent to Initial Investment	51
Land	280
Building and Improvements	201
Total Investment in Real Estate	481
Accumulated Depreciation and Amortization	$ 133
Date of Initial Leasehold or Acquisition Investment	1985