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Capitalization - Secondary Offering (Detail) - Class A common stock - Secondary Offering
$ / shares in Units, $ in Millions
 1 Months Ended 3 Months Ended
Mar. 31, 2017
$ / shares
shares
Mar. 31, 2017
USD ($)
$ / shares
Class of Stock [Line Items]    
Number of shares sold by selling shareholders 6,331,991  
Secondary offering price | $ / shares $ 35.50 $ 35.50
Additional shares purchase under option granted to underwriters 949,798  
Offering costs incurred | $   $ 0.9