Reclassifications out of Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 944.4
Other comprehensive income before reclassifications	(11.3)	$ (7.9)
Amounts reclassified from AOCL	0.7	(0.0)
Total other comprehensive loss	(10.6)	(7.9)
Ending Balance	958.6
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(57.3)	(74.4)
Ending Balance	(67.9)	(82.3)
Defined Benefit Pension Plan Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(15.9)	(9.3)
Other comprehensive income before reclassifications	0.0	0.0
Amounts reclassified from AOCL	0.7	(0.0)
Total other comprehensive loss	0.7	0.0
Ending Balance	(15.2)	(9.3)
Foreign Currency Translation Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(41.4)	(65.1)
Other comprehensive income before reclassifications	(11.3)	(7.9)
Amounts reclassified from AOCL	(0.0)	(0.0)
Total other comprehensive loss	(11.3)	(7.9)
Ending Balance	$ (52.7)	$ (73.0)