Financial Instruments - Financial Instruments not Carried at Fair Value but which Require Fair Value Disclosure (Detail) - USD ($) $ in Millions |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|---|---|---|---|---|
| Fair Value Disclosures [Abstract] | ||||
| Cash, cash equivalents and restricted cash, Carrying amount | $ 52.3 | $ 94.3 | ||
| Variable rate term loan, Carrying amount | 335.9 | 338.0 | ||
| Common stockholders' equity, Carrying amount | 395.0 | 461.9 | $ 781.1 | $ 935.1 |
| Cash, cash equivalents and restricted cash, Fair value | 52.3 | 94.3 | ||
| Variable rate term loan, Fair value | 334.6 | 309.5 | ||
| Common stockholders' equity, Fair value | $ 1,383.8 | $ 653.6 |