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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]
3 Months Ended
Mar. 31, 2017
$ / shares
shares
Nonvested Restricted Share Awards  
Beginning Balance | shares 683,667
Vested | shares (305,136)
Forfeited | shares (5,536)
Change in attainment for 2015 grants | shares (13,592)
Ending Balance | shares 359,403
Weighted-Average Grant Date Fair Value  
Beginning Balance | $ / shares $ 23.25
Vested | $ / shares 21.89
Forfeited | $ / shares 23.21
Change in attainment for 2015 grants | $ / shares 23.25
Ending Balance | $ / shares $ 24.41