Fair Value (Narrative) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|---|
Sep. 30, 2024 |
Sep. 30, 2023 |
Jun. 30, 2024 |
Sep. 30, 2024 |
Sep. 30, 2023 |
Dec. 31, 2023 |
|
| Fair Value Disclosure [Line Items] | ||||||
| Transfers between Fair Value Hierarchies | $ 0.0 | $ 0.0 | ||||
| Allowance for Credit Loss | $ 0.2 | 0.2 | $ 0.6 | |||
| Debt Securities, Available-for-Sale, Realized Gain | 0.1 | $ 0.0 | 0.5 | $ 0.6 | ||
| U.S. Treasury debt securities | ||||||
| Fair Value Disclosure [Line Items] | ||||||
| Allowance for Credit Loss | 0.0 | 0.0 | 0.0 | |||
| Available-for-sale Securities, Maturities, Next Twelve Months, Fair Value | 16.8 | |||||
| Corporate/Other debt securities | ||||||
| Fair Value Disclosure [Line Items] | ||||||
| Allowance for Credit Loss | $ 0.2 | $ 0.2 | 0.6 | |||
| Available-for-sale Securities, Maturities, Next Twelve Months, Fair Value | $ 4.9 | |||||