Income Taxes - Reconciliation of Amount Computed by Applying the Federal Statutory Income Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Federal statutory tax on earnings before income taxes	$ 49.1	$ 35.9	$ 51.6
State income taxes, net of federal income tax benefit	5.4	2.5	4.0
Non-deductible officer's compensation	2.6	4.7	2.3
Change in enacted tax rates	0.0	(57.7)	0.1
Windfall deduction from equity compensation	(4.7)	(5.2)	(4.9)
Other	(1.1)	(0.1)	(2.4)
Income tax expense (benefit)	$ 51.3	$ (19.9)	$ 50.7