Reclassifications out of Accumulated Other Comprehensive Loss - Summary of Reclassifications out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications		$ 0.5
Defined Benefit Pension Plan Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications		0.5
Reclassification Out of Accumulated Other Comprehensive Income/(Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (0.3)	(0.6)
Income tax expense	0.0	0.1
Total reclassifications	(0.3)	(0.5)
Reclassification Out of Accumulated Other Comprehensive Income/(Loss) [Member] \| Defined Benefit Pension Plan Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service credit	$ (0.3)	$ (0.6)

Amount, before tax, of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

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-Publisher FASB
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Amount before tax of reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss).

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