Defined Benefit Plan (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Cash
Components of net periodic benefit cost
Deferred compensation, Rabbi Trust	$ 7.8		$ 6.1
Short-term Investments
Components of net periodic benefit cost
Deferred compensation, Rabbi Trust	4.2		$ 5.5
Defined Benefit Plans
Components of net periodic benefit cost
Service cost	0.7	$ 0.7
Interest cost	1.1	1.5
Expected return on plan assets	(2.4)	(2.4)
Amortization of unrecognized loss	1.4	0.9
Net periodic benefit cost	0.8	0.7
Amortization of unrecognized loss, tax	$ (0.3)	$ (0.2)