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Stock-Based Compensation Plans - Summary of Nonvested Performance Based Share Awards and Changes During Period (Detail) - Performance-Based Restricted Share Awards [Member] - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Nonvested Restricted Share Awards    
Beginning Balance 938,863  
Granted   978,365
Forfeited (67,397) (39,502)
Vested (169,567)  
Change in attainment for 2015 grants (18,232)  
Ending Balance 683,667 938,863
Weighted-Average Grant Date Fair Value    
Beginning Balance $ 23.42  
Granted   $ 23.45
Forfeited 22.34 24.24
Vested 24.41  
Change in attainment for 2015 grants 24.41  
Ending Balance $ 23.25 $ 23.42