Summary of Employee and Director Stock Option Highlights (Detail) - Employee And Director Stock Option - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
---|---|---|---|---|
Jun. 30, 2017 |
Jun. 30, 2016 |
Jun. 30, 2017 |
Jun. 30, 2016 |
|
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
Compensation expense | $ 2.8 | $ 1.9 | $ 4.6 | $ 3.5 |
Intrinsic value of stock options exercised | 5.6 | 4.7 | 10.1 | 6.0 |
Tax benefit recognized from stock option exercises | $ 2.2 | $ 1.7 | $ 3.9 | $ 2.1 |