Quarterly report pursuant to Section 13 or 15(d)

Investment in Joint Ventures - Additional Information (Detail)

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Investment in Joint Ventures - Additional Information (Detail) - Sovran HHF, Sovran HHF II, 191 III, SERS, Urban Box, McDonald, Merrick, RAP and N32 [Member] - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Schedule of Equity Method Investments [Line Items]        
Management and call center fee earned $ 2.0 $ 1.9 $ 5.8 $ 4.8
Minimum [Member]        
Schedule of Equity Method Investments [Line Items]        
Management and call center fee as a percentage of revenues     6.00%  
Maximum [Member]        
Schedule of Equity Method Investments [Line Items]        
Management and call center fee as a percentage of revenues     7.00%