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Stock-Based Compensation Plans - Summary of Nonvested LTIP Performance Shares (Detail) - LTIP Performance Shares [Member]
3 Months Ended
Mar. 31, 2019
$ / shares
shares
Number of Shares at Expected Attainment  
Beginning Balance | shares 540,697
Forfeited | shares (1,036)
Ending Balance | shares 539,661
Weighted-Average Grant Date Fair Value  
Beginning Balance | $ / shares $ 19.83
Forfeited | $ / shares 20.12
Ending Balance | $ / shares $ 19.83