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Related Party Transactions - Additional Information (Detail) - Smith, Gambrell & Russell, LLP [Member] - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Related Party Transaction [Line Items]      
Fees payable to Smith, Gambrell & Russell $ 0.1   $ 0.1
Amount due to Smith, Gambrell & Russell $ 0.0 $ 0.0