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Fair Value Disclosure (Narrative) (Details) - Level 1 - Fair value measurements, recurring - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Jun. 30, 2020 | Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |
Unrealized gain (loss) on equity securities | $ 0.4 | $ (0.5) | $ 1.6 | $ (0.1) |  |
Bellaire |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |
Unrealized gain (loss) on equity securities | $ 0.1 | $ 0.5 | $ 1.0 | $ 0.4 |  |
Carrying Value |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |
Equity securities cost |  |  |  |  | $ 2.0 |
Carrying Value | Bellaire |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |
Equity securities cost |  |  |  |  |  | $ 5.0

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