Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Summary of Disaggregated Revenues (Detail)

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Summary of Significant Accounting Policies - Summary of Disaggregated Revenues (Detail) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disaggregation Of Revenue [Line Items]                      
Rental income                 $ 502,474 $ 485,303 $ 428,121
Total operating revenues $ 138,265 $ 141,483 $ 138,008 $ 133,094 $ 133,078 $ 135,568 $ 132,784 $ 128,320 550,850 529,750 462,608
Management and Acquisition Fee Income [Member]                      
Disaggregation Of Revenue [Line Items]                      
Operating revenues other than rental income                 10,571 9,867 6,095
Revenues Related to Tenant Insurance [Member]                      
Disaggregation Of Revenue [Line Items]                      
Operating revenues other than rental income                 23,057 22,597 18,666
Other Operating Income [Member]                      
Disaggregation Of Revenue [Line Items]                      
Operating revenues other than rental income                 $ 14,748 $ 11,983 $ 9,726