Reclassifications out of Accumulated Other Comprehensive Loss - Summary of Reclassifications out of Accumulated Other Comprehensive Loss (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications	$ (0.8)
Defined Benefit Pension Plan Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications	(0.8)
Reclassification Out of Accumulated Other Comprehensive Income/(Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	0.9
Income tax expense	(0.1)
Total reclassifications	0.8
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	(1.1)
Amortization of actuarial net losses	$ 2.0