Income Taxes - Additional Information (Detail) - USD ($) $ in Millions |
3 Months Ended | ||
|---|---|---|---|
Mar. 31, 2018 |
Dec. 31, 2017 |
Mar. 31, 2017 |
|
| Components Of Income Tax Expense Benefit [Line Items] | |||
| Income tax effective rate | 50.70% | 242.80% | |
| Income tax expense (benefit) impact of the tax act | $ (0.5) | $ 8.3 | |
| Minimum [Member] | |||
| Components Of Income Tax Expense Benefit [Line Items] | |||
| Decrease in unrecognized tax benefits | 2.1 | ||
| Maximum [Member] | |||
| Components Of Income Tax Expense Benefit [Line Items] | |||
| Decrease in unrecognized tax benefits | $ 4.1 | ||