Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 12 (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Investments In Real Estate [Line Items]
Total Investment in Real Estate	$ 782,166	$ 783,233	$ 595,959	$ 570,275
Accumulated Depreciation And Amortization Description [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	720,099
Cost Capitalized Subsequent to Initial Investment	62,067
Land	474,232
Building and Improvements	307,934
Total Investment in Real Estate	782,166
Accumulated Depreciation and Amortization	120,576
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Emmitsburg One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	147
Cost Capitalized Subsequent to Initial Investment	191
Land	102
Building and Improvements	236
Total Investment in Real Estate	338
Accumulated Depreciation and Amortization	$ 154
Date of Initial Leasehold or Acquisition Investment	1986
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Forestville One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,039
Land	1,039
Total Investment in Real Estate	$ 1,039
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Fort Washington One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 422
Land	422
Total Investment in Real Estate	$ 422
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Greenbelt One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,153
Land	1,153
Total Investment in Real Estate	$ 1,153
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Hyattsville One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 491
Land	491
Total Investment in Real Estate	$ 491
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Hyattsville Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 594
Land	594
Total Investment in Real Estate	$ 594
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Landover One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 662
Land	662
Total Investment in Real Estate	$ 662
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Landover Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 753
Land	753
Total Investment in Real Estate	$ 753
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Landover Hills One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 457
Land	457
Total Investment in Real Estate	$ 457
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Landover Hills Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,358
Land	1,358
Total Investment in Real Estate	$ 1,358
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Lanham One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 822
Land	822
Total Investment in Real Estate	$ 822
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Laurel One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 696
Land	696
Total Investment in Real Estate	$ 696
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Laurel Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,210
Land	1,210
Total Investment in Real Estate	$ 1,210
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Laurel Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,267
Land	1,267
Total Investment in Real Estate	$ 1,267
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Laurel Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,415
Land	1,415
Total Investment in Real Estate	$ 1,415
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Laurel Five [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,530
Land	1,530
Total Investment in Real Estate	$ 1,530
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Laurel Six [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,523
Land	2,523
Total Investment in Real Estate	$ 2,523
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Oxon Hill One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,256
Land	1,256
Total Investment in Real Estate	$ 1,256
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Riverdale One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 582
Land	582
Total Investment in Real Estate	$ 582
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Riverdale Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 788
Land	788
Total Investment in Real Estate	$ 788
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Seat Pleasant One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 468
Land	468
Total Investment in Real Estate	$ 468
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Suitland One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 377
Land	377
Total Investment in Real Estate	$ 377
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Suitland Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 673
Land	673
Total Investment in Real Estate	$ 673
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Temple Hills One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 331
Land	331
Total Investment in Real Estate	$ 331
Date of Initial Leasehold or Acquisition Investment	2009
MARYLAND | Accumulated Depreciation And Amortization Description [Member] | Upper Marlboro One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 845
Land	845
Total Investment in Real Estate	$ 845
Date of Initial Leasehold or Acquisition Investment	2009
MAINE | Accumulated Depreciation And Amortization Description [Member] | Biddeford One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 618
Cost Capitalized Subsequent to Initial Investment	8
Land	235
Building and Improvements	391
Total Investment in Real Estate	626
Accumulated Depreciation and Amortization	$ 391
Date of Initial Leasehold or Acquisition Investment	1985
MAINE | Accumulated Depreciation And Amortization Description [Member] | Lewiston One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 342
Cost Capitalized Subsequent to Initial Investment	188
Land	222
Building and Improvements	308
Total Investment in Real Estate	530
Accumulated Depreciation and Amortization	$ 200
Date of Initial Leasehold or Acquisition Investment	1985
NORTH CAROLINA | Accumulated Depreciation And Amortization Description [Member] | Kernersville One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 449
Land	338
Building and Improvements	111
Total Investment in Real Estate	449
Accumulated Depreciation and Amortization	$ 102
Date of Initial Leasehold or Acquisition Investment	2007
NORTH CAROLINA | Accumulated Depreciation And Amortization Description [Member] | Madison One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 396
Land	46
Building and Improvements	350
Total Investment in Real Estate	396
Accumulated Depreciation and Amortization	$ 185
Date of Initial Leasehold or Acquisition Investment	2007