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Stock-Based Compensation Plans - Summary of Stock Options Issued Pursuant to Stock Incentive Plans (Detail)
 9 Months Ended
Sep. 30, 2017
USD ($)
$ / shares
shares
Number of Shares  
Outstanding, Beginning Balance | shares 6,791,375
Granted | shares 864,800
Exercised | shares (756,140)
Forfeited | shares (207,559)
Expired | shares (17,507)
Outstanding, Ending Balance | shares 6,674,969
Number of Shares Exercisable, Ending Balance | shares 3,938,286
Weighted-Average Exercise Price  
Beginning Balance | $ / shares $ 15.54
Granted | $ / shares 20.12
Exercised | $ / shares 13.60
Forfeited | $ / shares 18.46
Expired | $ / shares 20.36
Ending Balance | $ / shares 16.25
Weighted-Average Exercise Price Exercisable, Ending Balance | $ / shares $ 14.45
Weighted-Average Remaining Contractual Term (Years)  
Weighted Average Remaining Contractual Term (Years), Outstanding as of end of period 6 years 7 months 6 days
Weighted-Average Remaining Contractual Term (Years), Exercisable as of end of period 5 years 3 months 22 days
Aggregate Intrinsic Value of In-the-Money Options  
Aggregate Intrinsic Value of In-the-Money Options, Outstanding as of end of period | $ $ 43,563,796
Aggregate Intrinsic Value of In-the-Money Options, Exercisable as of end of period | $ $ 32,792,014