Retirement Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss included in accumulated other comprehensive income (loss) expected to be recognized in net periodic benefit cost, before tax	$ (0.7)
Defined contribution plan, total costs	$ 5.0	$ 5.3	$ 5.3