Schedule III - Real Estate and Accumulated Depreciation and Amortization Part 3 (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
CALIFORNIA [Member] | Accumulated Depreciation And Amortization Description [Member] | Sacramento Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	4,247
Land	2,604
Building and Improvements	1,643
Total Investment in Real Estate	4,247
Accumulated Depreciation and Amortization	$ 247
Date of Initial Leasehold or Acquisition Investment	2015
CALIFORNIA [Member] | Accumulated Depreciation And Amortization Description [Member] | Sacramento Three
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 5,942
Land	4,233
Building and Improvements	1,709
Total Investment in Real Estate	5,942
Accumulated Depreciation and Amortization	$ 275
Date of Initial Leasehold or Acquisition Investment	2015
CALIFORNIA [Member] | Accumulated Depreciation And Amortization Description [Member] | SanDimas One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,941
Land	749
Building and Improvements	1,192
Total Investment in Real Estate	1,941
Accumulated Depreciation and Amortization	$ 573
Date of Initial Leasehold or Acquisition Investment	2007
CALIFORNIA [Member] | Accumulated Depreciation And Amortization Description [Member] | San Jose One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 5,412
Land	4,219
Building and Improvements	1,193
Total Investment in Real Estate	5,412
Accumulated Depreciation and Amortization	$ 214
Date of Initial Leasehold or Acquisition Investment	2015
CALIFORNIA [Member] | Accumulated Depreciation And Amortization Description [Member] | San Leandro One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 5,978
Land	5,078
Building and Improvements	900
Total Investment in Real Estate	5,978
Accumulated Depreciation and Amortization	$ 159
Date of Initial Leasehold or Acquisition Investment	2015
CALIFORNIA [Member] | Accumulated Depreciation And Amortization Description [Member] | Shingle Springs One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 4,751
Land	3,489
Building and Improvements	1,262
Total Investment in Real Estate	4,751
Accumulated Depreciation and Amortization	$ 209
Date of Initial Leasehold or Acquisition Investment	2015
CALIFORNIA [Member] | Accumulated Depreciation And Amortization Description [Member] | Stockton One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,187
Land	627
Building and Improvements	560
Total Investment in Real Estate	1,187
Accumulated Depreciation and Amortization	$ 95
Date of Initial Leasehold or Acquisition Investment	2015
CALIFORNIA [Member] | Accumulated Depreciation And Amortization Description [Member] | Stockton Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,001
Land	1,460
Building and Improvements	1,541
Total Investment in Real Estate	3,001
Accumulated Depreciation and Amortization	$ 236
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Wheat Ridge One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 6,151
Land	4,201
Building and Improvements	1,950
Total Investment in Real Estate	6,151
Accumulated Depreciation and Amortization	$ 321
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Adams [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,157
Land	1,579
Building and Improvements	578
Total Investment in Real Estate	2,157
Accumulated Depreciation and Amortization	$ 13
Date of Initial Leasehold or Acquisition Investment	2017
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Aurora [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,874
Land	2,284
Building and Improvements	590
Total Investment in Real Estate	2,874
Accumulated Depreciation and Amortization	$ 12
Date of Initial Leasehold or Acquisition Investment	2017
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Boulder One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,900
Land	2,875
Building and Improvements	1,025
Total Investment in Real Estate	3,900
Accumulated Depreciation and Amortization	$ 154
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Broomfield One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,380
Land	1,496
Building and Improvements	884
Total Investment in Real Estate	2,380
Accumulated Depreciation and Amortization	$ 17
Date of Initial Leasehold or Acquisition Investment	2017
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Broomfield Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,785
Land	1,388
Building and Improvements	397
Total Investment in Real Estate	1,785
Accumulated Depreciation and Amortization	$ 9
Date of Initial Leasehold or Acquisition Investment	2017
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Castle Rock [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 5,269
Land	3,269
Building and Improvements	2,000
Total Investment in Real Estate	5,269
Accumulated Depreciation and Amortization	$ 322
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Colorado Springs One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,382
Land	756
Building and Improvements	626
Total Investment in Real Estate	1,382
Accumulated Depreciation and Amortization	$ 12
Date of Initial Leasehold or Acquisition Investment	2017
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Colorado Springs Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,274
Land	2,865
Building and Improvements	409
Total Investment in Real Estate	3,274
Accumulated Depreciation and Amortization	$ 9
Date of Initial Leasehold or Acquisition Investment	2017
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Colorado Springs Three [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,828
Land	2,798
Building and Improvements	1,030
Total Investment in Real Estate	3,828
Accumulated Depreciation and Amortization	$ 23
Date of Initial Leasehold or Acquisition Investment	2017
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Denver [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 1,457
Land	752
Building and Improvements	705
Total Investment in Real Estate	1,457
Accumulated Depreciation and Amortization	$ 110
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Englewood [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,495
Land	2,207
Building and Improvements	288
Total Investment in Real Estate	2,495
Accumulated Depreciation and Amortization	$ 7
Date of Initial Leasehold or Acquisition Investment	2017
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Golden One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 4,641
Land	3,247
Building and Improvements	1,394
Total Investment in Real Estate	4,641
Accumulated Depreciation and Amortization	$ 218
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Greenwood Village One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 4,077
Land	2,889
Building and Improvements	1,188
Total Investment in Real Estate	4,077
Accumulated Depreciation and Amortization	$ 178
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Highlands Ranch One
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 4,356
Land	2,921
Building and Improvements	1,435
Total Investment in Real Estate	4,356
Accumulated Depreciation and Amortization	$ 229
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Lakewood One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 2,349
Land	1,541
Building and Improvements	808
Total Investment in Real Estate	2,349
Accumulated Depreciation and Amortization	$ 123
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Littleton One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 4,233
Land	2,366
Building and Improvements	1,867
Total Investment in Real Estate	4,233
Accumulated Depreciation and Amortization	$ 297
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Lone Tree One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 6,612
Land	5,125
Building and Improvements	1,487
Total Investment in Real Estate	6,612
Accumulated Depreciation and Amortization	$ 248
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Longmont One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,619
Land	2,315
Building and Improvements	1,304
Total Investment in Real Estate	3,619
Accumulated Depreciation and Amortization	$ 217
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Louisville One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 6,605
Land	5,228
Building and Improvements	1,377
Total Investment in Real Estate	6,605
Accumulated Depreciation and Amortization	$ 225
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Morrison One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 5,081
Land	3,018
Building and Improvements	2,063
Total Investment in Real Estate	5,081
Accumulated Depreciation and Amortization	$ 340
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Superior One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 3,748
Land	2,477
Building and Improvements	1,271
Total Investment in Real Estate	3,748
Accumulated Depreciation and Amortization	$ 202
Date of Initial Leasehold or Acquisition Investment	2015
COLORADO | Accumulated Depreciation And Amortization Description [Member] | Thornton One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 5,003
Land	2,722
Building and Improvements	2,281
Total Investment in Real Estate	5,003
Accumulated Depreciation and Amortization	$ 364
Date of Initial Leasehold or Acquisition Investment	2015
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Avon One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 731
Cost Capitalized Subsequent to Initial Investment	167
Land	403
Building and Improvements	495
Total Investment in Real Estate	898
Accumulated Depreciation and Amortization	$ 266
Date of Initial Leasehold or Acquisition Investment	2002
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Bridgeport One [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 59
Cost Capitalized Subsequent to Initial Investment	380
Land	24
Building and Improvements	415
Total Investment in Real Estate	439
Accumulated Depreciation and Amortization	$ 224
Date of Initial Leasehold or Acquisition Investment	1982
CONNECTICUT [Member] | Accumulated Depreciation And Amortization Description [Member] | Bridgeport Two [Member]
Schedule Of Investments In Real Estate [Line Items]
Initial Cost of Leasehold or Acquisition Investment to Company	$ 313
Cost Capitalized Subsequent to Initial Investment	298
Land	204
Building and Improvements	407
Total Investment in Real Estate	611
Accumulated Depreciation and Amortization	$ 193
Date of Initial Leasehold or Acquisition Investment	1985