Annual report pursuant to Section 13 and 15(d)

Real Estate and Intangible Assets - Components of Investments in Real Estate (Detail)

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Real Estate and Intangible Assets - Components of Investments in Real Estate (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Real estate:      
Land $ 121,783 $ 104,719  
Building and improvements 708,948 662,661  
Tenant improvements 63,122 54,369  
Accumulated depreciation (149,417) (131,661)  
Total real estate, net 744,436 690,088  
Building and Improvements      
Real Estate Properties [Line Items]      
Depreciation $ 26,900 $ 24,100 $ 22,200