Organization - Use of the Proceeds from the IPO (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Consolidation, Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] | |||
| Gross proceeds | $ 631.3 | ||
| Underwriters' discount and commissions | 29.2 | ||
| IPO-related expenses | 11.8 | ||
| Redemption of 11% Senior Notes due 2021 (Note 9) | 1,134.0 | $ 25.9 | $ 11.8 |
| Sponsor management fee | 11.3 | ||
| Debt refinancing expenses | 11.4 | ||
| Cash to balance sheet | 68.6 | ||
| Senior Notes [Member] | 11% Senior Note [Member] | |||
| Consolidation, Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] | |||
| Redemption of 11% Senior Notes due 2021 (Note 9) | 475.0 | ||
| Call premium on redemption of 11% Senior Notes due 2021 | 13.1 | ||
| Interest on redemption of 11% Senior Notes due 2021 | $ 10.9 | ||