Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 8 (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
HAWAII | Accumulated Depreciation And Amortization Description [Member] | Haleiwa One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	1,522
Land	1,058
Building and Improvements	464
Total Investment in Real Estate	1,522
Accumulated Depreciation and Amortization	$ 300
Date of Initial Leasehold or Acquisition Investment	2007
HAWAII | Accumulated Depreciation And Amortization Description [Member] | Honolulu One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,069
Cost Capitalized Subsequent to Initial Investment	16
Land	981
Building and Improvements	104
Total Investment in Real Estate	1,085
Accumulated Depreciation and Amortization	$ 75
Date of Initial Leasehold or Acquisition Investment	2007
HAWAII | Accumulated Depreciation And Amortization Description [Member] | Honolulu Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,539
Land	1,219
Building and Improvements	320
Total Investment in Real Estate	1,539
Accumulated Depreciation and Amortization	$ 162
Date of Initial Leasehold or Acquisition Investment	2007
HAWAII | Accumulated Depreciation And Amortization Description [Member] | Honolulu Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,769
Land	1,192
Building and Improvements	577
Total Investment in Real Estate	1,769
Accumulated Depreciation and Amortization	$ 269
Date of Initial Leasehold or Acquisition Investment	2007
HAWAII | Accumulated Depreciation And Amortization Description [Member] | Honolulu Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 9,211
Land	8,194
Building and Improvements	1,017
Total Investment in Real Estate	9,211
Accumulated Depreciation and Amortization	$ 490
Date of Initial Leasehold or Acquisition Investment	2007
HAWAII | Accumulated Depreciation And Amortization Description [Member] | Kaneohe One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,364
Land	822
Building and Improvements	542
Total Investment in Real Estate	1,364
Accumulated Depreciation and Amortization	$ 295
Date of Initial Leasehold or Acquisition Investment	2007
HAWAII | Accumulated Depreciation And Amortization Description [Member] | Kaneohe Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,978
Cost Capitalized Subsequent to Initial Investment	182
Land	1,473
Building and Improvements	687
Total Investment in Real Estate	2,160
Accumulated Depreciation and Amortization	$ 297
Date of Initial Leasehold or Acquisition Investment	2007
HAWAII | Accumulated Depreciation And Amortization Description [Member] | Waianae One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,520
Land	648
Building and Improvements	872
Total Investment in Real Estate	1,520
Accumulated Depreciation and Amortization	$ 406
Date of Initial Leasehold or Acquisition Investment	2007
HAWAII | Accumulated Depreciation And Amortization Description [Member] | Waianae Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,997
Land	871
Building and Improvements	1,126
Total Investment in Real Estate	1,997
Accumulated Depreciation and Amortization	$ 527
Date of Initial Leasehold or Acquisition Investment	2007
HAWAII | Accumulated Depreciation And Amortization Description [Member] | Waipahu One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,458
Land	945
Building and Improvements	1,513
Total Investment in Real Estate	2,458
Accumulated Depreciation and Amortization	$ 676
Date of Initial Leasehold or Acquisition Investment	2007
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Arlington One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 518
Cost Capitalized Subsequent to Initial Investment	28
Land	338
Building and Improvements	208
Total Investment in Real Estate	546
Accumulated Depreciation and Amortization	$ 164
Date of Initial Leasehold or Acquisition Investment	1985
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Auburn One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 174
Cost Capitalized Subsequent to Initial Investment	213
Land	125
Building and Improvements	262
Total Investment in Real Estate	387
Accumulated Depreciation and Amortization	$ 122
Date of Initial Leasehold or Acquisition Investment	1986
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Auburn Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Cost Capitalized Subsequent to Initial Investment	$ 535
Land	388
Building and Improvements	147
Total Investment in Real Estate	535
Accumulated Depreciation and Amortization	$ 29
Date of Initial Leasehold or Acquisition Investment	1996
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Auburn Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 600
Land	600
Total Investment in Real Estate	$ 600
Date of Initial Leasehold or Acquisition Investment	2011
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Auburn Four [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 625
Land	625
Total Investment in Real Estate	$ 625
Date of Initial Leasehold or Acquisition Investment	2011
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Auburn Five [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 369
Cost Capitalized Subsequent to Initial Investment	264
Land	240
Building and Improvements	393
Total Investment in Real Estate	633
Accumulated Depreciation and Amortization	$ 182
Date of Initial Leasehold or Acquisition Investment	1991
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Auburn Six [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 725
Land	725
Total Investment in Real Estate	$ 725
Date of Initial Leasehold or Acquisition Investment	2011
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Auburn Seven [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 800
Building and Improvements	800
Total Investment in Real Estate	800
Accumulated Depreciation and Amortization	$ 442
Date of Initial Leasehold or Acquisition Investment	2011
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Barre One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 536
Cost Capitalized Subsequent to Initial Investment	12
Land	348
Building and Improvements	200
Total Investment in Real Estate	548
Accumulated Depreciation and Amortization	$ 111
Date of Initial Leasehold or Acquisition Investment	1991
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Bedford One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,350
Land	1,350
Total Investment in Real Estate	$ 1,350
Date of Initial Leasehold or Acquisition Investment	2011
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Bellingham One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 734
Cost Capitalized Subsequent to Initial Investment	73
Land	476
Building and Improvements	331
Total Investment in Real Estate	807
Accumulated Depreciation and Amortization	$ 269
Date of Initial Leasehold or Acquisition Investment	1985
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Belmont One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 390
Cost Capitalized Subsequent to Initial Investment	29
Land	254
Building and Improvements	165
Total Investment in Real Estate	419
Accumulated Depreciation and Amortization	$ 132
Date of Initial Leasehold or Acquisition Investment	1985
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Bradford One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 650
Land	650
Total Investment in Real Estate	$ 650
Date of Initial Leasehold or Acquisition Investment	2011
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Burlington One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 600
Land	600
Total Investment in Real Estate	$ 600
Date of Initial Leasehold or Acquisition Investment	2011
MASSACHUSETTS | Accumulated Depreciation And Amortization Description [Member] | Burlington Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,250
Land	1,250
Total Investment in Real Estate	$ 1,250
Date of Initial Leasehold or Acquisition Investment	2011