Employee Benefits - Plan Assets and Investment Policy (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Employee Benefits
Weighted-average asset allocations (as a percent)	100.00%	100.00%
Defined Benefit Plan
Employee Benefits
Total investments at fair value	$ 63.8	$ 56.7	$ 70.9
Defined Benefit Plan | Level 1
Employee Benefits
Total investments at fair value	51.7	46.1
Defined Benefit Plan | Level 2
Employee Benefits
Total investments at fair value	12.1	10.6
Defined Benefit Plan | Common stock.
Employee Benefits
Fair value of plan assets	37.8	31.4
Defined Benefit Plan | Common stock. | Level 1
Employee Benefits
Fair value of plan assets	37.8	31.4
Defined Benefit Plan | U.S. government, state, and agency
Employee Benefits
Fair value of plan assets	8.3	6.0
Defined Benefit Plan | U.S. government, state, and agency | Level 2
Employee Benefits
Fair value of plan assets	8.3	6.0
Defined Benefit Plan | Corporate debt securities
Employee Benefits
Fair value of plan assets	3.8	4.6
Defined Benefit Plan | Corporate debt securities | Level 2
Employee Benefits
Fair value of plan assets	3.8	4.6
Defined Benefit Plan | Mutual funds
Employee Benefits
Fair value of plan assets	13.4	12.6
Defined Benefit Plan | Mutual funds | Level 1
Employee Benefits
Fair value of plan assets	13.4	12.6
Defined Benefit Plan | Interest bearing cash
Employee Benefits
Fair value of plan assets	0.5	2.1
Defined Benefit Plan | Interest bearing cash | Level 1
Employee Benefits
Fair value of plan assets	$ 0.5	$ 2.1
Common stock.
Employee Benefits
Weighted-average asset allocations (as a percent)	62.00%	58.00%
Debt securities
Employee Benefits
Weighted-average asset allocations (as a percent)	37.00%	38.00%
Interest bearing cash
Employee Benefits
Weighted-average asset allocations (as a percent)	1.00%	4.00%