Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 7 (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] | 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	$ 86
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	$ 95
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	$ 804
Land	516
Building and Improvements	288
Total Investment in Real Estate	804
Accumulated Depreciation and Amortization	$ 156
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	$ 163
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	$ 213
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	$ 242
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	$ 224
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	$ 180
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	$ 132
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	215
Land	338
Building and Improvements	396
Total Investment in Real Estate	734
Accumulated Depreciation and Amortization	$ 273
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	$ 190
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	$ 1,468
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	$ 100
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	$ 74
Date of Initial Leasehold or Acquisition Investment	2013
FLORIDA [Member] | Accumulated Depreciation And Amortization Description [Member] | Callahan [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,894
Land	2,056
Building and Improvements	838
Total Investment in Real Estate	2,894
Accumulated Depreciation and Amortization	$ 18
Date of Initial Leasehold or Acquisition Investment	2017