Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward | |||
| Balance at beginning of year | $ 1.0 | $ 0.7 | $ 1.3 |
| Additions for tax positions of the current year | 0.0 | 0.3 | 0.0 |
| Additions for tax positions of prior years | 0.9 | 0.0 | 0.0 |
| Settlements during the year | 0.0 | 0.0 | (0.5) |
| Lapses of applicable statutes of limitations | 0.0 | 0.0 | (0.1) |
| Balance at end of year | $ 1.9 | $ 1.0 | $ 0.7 |