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Stock-Based Compensation Plans - Summary of Nonvested Total Shareholder Return (TSRs) Outstanding and Changes During Period (Detail) - Total Shareholder Return [Member]
6 Months Ended
Jun. 30, 2017
$ / shares
shares
Number of shares at expected attainment  
Granted | shares 233,077
Forfeited | shares (8,624)
Ending Balance | shares 224,453
Weighted-Average Grant Date Fair Value  
Granted | $ / shares $ 24.37
Forfeited | $ / shares 24.37
Ending Balance | $ / shares $ 24.37