Employee Retirement Plans - Amounts recognized in other comprehensive income (loss) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Actuarial (loss) gain	$ (12.5)	$ 5.2	$ (5.3)
Amortization of actuarial loss	4.8	4.9	5.1
Total before income taxes	(7.7)	10.1	(0.2)
Income tax (benefit) expense	(1.8)	3.1	(0.1)
Net amount recognized in other comprehensive (loss) income	$ (5.9)	$ 7.0	$ (0.1)

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Amount, before tax, after reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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Amount, before tax, of gain (loss) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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