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Stock-Based Compensation - Summarizes Information of Performance Share Awards (Detail) - Performance Awards
12 Months Ended
Dec. 31, 2018
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Non-vested at December 31, 2017 | shares 428,328
Granted | shares 140,071
Vested | shares (136,822)
Forfeited | shares (22,486)
Non-vested at December 31, 2018 | shares 409,091
Non-vested at December 31, 2017 | $ / shares $ 52.35
Granted | $ / shares 63.44
Vested | $ / shares 47.48
Forfeited | $ / shares 57.41
Non-vested at December 31, 2018 | $ / shares $ 57.50