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Share-Based Compensation - Summary of RSUs Outstanding Under LTIP (Detail)
9 Months Ended
Sep. 30, 2017
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Nonvested as of January 1, 2017 146,142
Granted 90,807
Vested 0
Forfeited (12,304)
Nonvested as of September 30, 2017 224,645
Nonvested as of January 1, 2017, Weighted-Average Grant-Date Fair Value | $ / shares $ 38.46
Weighted-Average Grant-Date Fair Value, Granted | $ / shares 54.60
Weighted-Average Grant-Date Fair Value, Vested | $ / shares 0.00
Weighted-Average Grant-Date Fair Value, Forfeited | $ / shares 46.86
Nonvested as of September 30, 2017, Weighted-Average Grant-Date Fair Value | $ / shares $ 44.53
Performance Required [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Nonvested as of January 1, 2017 130,168
Granted 80,247
Vested 0
Forfeited (9,843)
Nonvested as of September 30, 2017 200,572
Service Required [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Nonvested as of January 1, 2017 15,974
Granted 10,560
Vested 0
Forfeited (2,461)
Nonvested as of September 30, 2017 24,073