Changes in Accumulated Other Comprehensive Income (Loss) - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Actuarial gains (losses), net of tax	$ (5.0)	$ 1.3	$ (3.0)
Actuarial (losses) gains, tax expense (benefit)	(1.5)	0.1	(1.6)
Amortization of actuarial losses, net of tax	0.8	0.7	0.6
Amortization of actuarial losses, tax expense (benefit)	$ (0.2)	$ (0.4)	$ (0.4)