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CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Unrealized net (loss) gain on cash flow derivative instruments, related income tax benefit (provision) | $ 0.7 | $ 0.6 | $ (0.2)
Change in pension liability, related income tax (provision) benefit | (7.5) | 5.7 | (0.5)
Accumulated Other Comprehensive Loss |  |  |
Unrealized net (loss) gain on cash flow derivative instruments, related income tax benefit (provision) | 0.7 | 0.6 | (0.2)
Change in pension liability, related income tax (provision) benefit | $ (7.5) | $ 5.7 | $ (0.5)
Treasury Stock |  |  |
Exercise of stock options, shares surrendered as proceeds and to pay taxes | 160,856 | 54,019 | 418,754

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