Accumulated Other Comprehensive Income (Loss) - Accumulated Other Comprehensive Income (Loss) Activity (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss)
Balance, beginning of year	$ (7.1)	$ (1.0)
Currency translation adjustments	10.5	(2.3)	$ (6.0)
Pension benefit adjustments	1.5	(5.1)	7.1
Deferred tax benefit (expense) on pension benefit adjustment	(0.4)	1.5	(2.1)
Amortization of net actuarial gains		(0.3)
Income tax on amortization of net actuarial gains		0.1
Balance, end of year	4.5	(7.1)	(1.0)
Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss)
Balance, beginning of year	(8.2)	(6.0)
Currency translation adjustments	10.5	(2.2)
Balance, end of year	2.3	(8.2)	(6.0)
Pension Benefit Adjustments
Accumulated Other Comprehensive Income (Loss)
Balance, beginning of year	1.1	5.0
Currency translation adjustments		(0.1)
Pension benefit adjustments	1.5	(5.1)
Deferred tax benefit (expense) on pension benefit adjustment	(0.4)	1.5
Amortization of net actuarial gains		(0.3)
Income tax on amortization of net actuarial gains		0.1
Balance, end of year	$ 2.2	$ 1.1	$ 5.0