Provisions for Federal and State Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current Income Tax Provision
Federal	$ 4.3	$ 0.2	$ 0.0
State	1.5	0.2	0.7
Total Current Income Taxes	5.8	0.2	0.7
Deferred Income Tax Provision
Federal	4.8	6.6	7.3
State	2.6	4.4	3.5
Total Deferred Income Taxes	7.4	11.0	10.8
Total Income Tax Expense	$ 13.2	$ 11.2	$ 11.5