Annual report pursuant to Section 13 and 15(d)

Schedule III - Real Estate and Accumulated Depreciation - Change in Balance of Accumulated Depreciation (Detail)

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Schedule III - Real Estate and Accumulated Depreciation - Change in Balance of Accumulated Depreciation (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
SEC Schedule III, Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]      
Balance at beginning of period $ 134,329 $ 113,089 $ 92,133
Additions during period 26,927 24,148 22,220
Dispositions during period (7,869) (2,908) (1,264)
Balance at end of period $ 153,387 $ 134,329 $ 113,089