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Stock-Based Compensation Plans - Summary of Nonvested TSRs (Detail) - Total Shareholder Return [Member]
12 Months Ended
Dec. 31, 2018
$ / shares
shares
Number of Shares at Expected Attainment  
Beginning Balance | shares 143,649
Granted | shares 541,214
Forfeited | shares (42,855)
Change in attainment | shares 76,923
Ending Balance | shares 718,931
Weighted-Average Grant Date Fair Value  
Beginning Balance | $ / shares $ 24.37
Granted | $ / shares 31.31
Forfeited | $ / shares 30.19
Change in attainment | $ / shares 24.37
Ending Balance | $ / shares $ 29.25