Annual report pursuant to Section 13 and 15(d)

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

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Schedule III - Real Estate and Accumulated Depreciation - Change in Balance of Real Estate (Detail) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
SEC Schedule III, Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]        
Balance at beginning of period $ 833,203 $ 833,203 $ 782,276 $ 722,565
Additions:        
Acquisitions during period   100,103 52,719 60,231
Improvements   10,473 10,362 6,527
Deductions:        
Dispositions during period   (30,094) (10,138) (6,425)
Impairments during period $ (3,700) (6,835) (2,016) (622)
Balance at end of period   $ 906,850 $ 833,203 $ 782,276