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Share-Based Compensation Plans - Summary of Activity Related to Restricted Stock Granted under Incentive Plan (Detail) - Restricted Stock Grants [Member] - $ / shares
shares in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total Shares, Outstanding, Beginning Balance 993 1,056 1,033
Total Shares, Granted 192 275 324
Total Shares, Vested (375) (329) (274)
Total Shares, Forfeited, canceled or expired (34) (9) (27)
Total Shares, Outstanding, Ending Balance 776 993 1,056
Weighted Average Grant Date Fair Value, Beginning Balance $ 38.32 $ 34.30 $ 28.75
Weighted Average Grant Date Fair Value, Granted 70.44 44.46 45.66
Weighted Average Grant Date Fair Value, Vested 32.46 30.56 27.18
Weighted Average Grant Date Fair Value, Forfeited, cancelled or expired 44.51 37.94 30.27
Weighted Average Grant Date Fair Value, Ending Balance $ 49.16 $ 38.32 $ 34.30