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Operating Leases - Narrative (Detail)
$ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2017
ft²
location
Dec. 31, 2016
USD ($)
Leases [Abstract]    
Area of operating lease | ft² 37,829  
Number of office space locations | location 1  
Operating lease expense excluding rent | $   $ 0.4