Income Taxes - Reconciliation of Amount Computed by Applying the Federal Statutory Income Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Federal statutory tax on earnings before income taxes	$ 41.2	$ 49.1	$ 35.9
State income taxes, net of federal income tax benefit	8.0	5.4	2.5
Non-deductible officer's compensation	5.5	2.6	4.7
Re-measurement of deferred taxes	8.3	0.0	(57.7)
Windfall deduction from equity compensation	(5.2)	(4.7)	(5.2)
Other	(1.0)	(1.1)	(0.1)
Income tax expense (benefit)	$ 56.8	$ 51.3	$ (19.9)