v3.8.0.1
Summary of Significant Accounting Policies - Schedule Showing Reduction of Carrying Value of Impaired Real Estate Assets to Estimated Fair Value (Detail) - USD ($)
$ in Thousands
Dec. 31, 2017
Sep. 30, 2017
Dec. 31, 2016
Significant Accounting Policies [Line Items]      
Investments in rental property accounted for using the operating method, net of accumulated depreciation $ 2,227,758   $ 1,684,971
Intangible lease assets, net 242,659   168,121
Leasing fees, net 13,554   11,329
Intangible lease liabilities, net $ (81,744)   $ (47,871)
Carrying Amount      
Significant Accounting Policies [Line Items]      
Investments in rental property accounted for using the operating method, net of accumulated depreciation   $ 16,159  
Intangible lease assets, net   1,263  
Leasing fees, net   123  
Intangible lease liabilities, net   (101)  
Impaired real estate assets (liabilities), net   17,444  
Allocation of impairment      
Significant Accounting Policies [Line Items]      
Investments in rental property accounted for using the operating method, net of accumulated depreciation   (2,401)  
Intangible lease assets, net   (204)  
Leasing fees, net   (16)  
Intangible lease liabilities, net   13  
Impaired real estate assets (liabilities), net   (2,608)  
Net Carrying Amount      
Significant Accounting Policies [Line Items]      
Investments in rental property accounted for using the operating method, net of accumulated depreciation   13,758  
Intangible lease assets, net   1,059  
Leasing fees, net   107  
Intangible lease liabilities, net   (88)  
Impaired real estate assets (liabilities), net   $ 14,836