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Benefit Plans - Allocation of Plan Assets (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 100.00% | 100.00%
Fair value of plan assets | $ 258.1 | $ 244.1
Pension plan assets in the fair value hierarchy |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 43.7 | 39.4
Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 1.5 | 7.3
Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 42.2 | 32.1
Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 0.0 |
Pension plan assets measured at NAV |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 214.4 | 204.7
Cash | Pension plan assets in the fair value hierarchy |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 1.5 | 2.2
Cash | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 1.5 | 2.2
Cash | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 0.0 | 0.0
Cash | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | $ 0.0 | $ 0.0
Equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 34.00% | 33.00%
Equity securities | United States |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 30.00% |
Equity securities | Pension plan assets in the fair value hierarchy |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | $ 20.6 | $ 15.5
Equity securities | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 0.0 | 1.3
Equity securities | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 20.6 | 14.2
Equity securities | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | $ 0.0 | $ 0.0
Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 64.00% | 65.00%
Debt securities | United States |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 70.00% |
Other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 2.00% | 2.00%
Other | United States |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 0.00% |
Mutual funds | Pension plan assets in the fair value hierarchy |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | $ 18.7 | $ 21.7
Mutual funds | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 0.0 | 3.8
Mutual funds | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 18.7 | 17.9
Mutual funds | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 0.0 | $ 0.0
Other mutual funds | Pension plan assets in the fair value hierarchy |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 2.9 |
Other mutual funds | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 0.0 |
Other mutual funds | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | 2.9 |
Other mutual funds | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Fair value of plan assets | $ 0.0 |
Minimum | Equity securities | United States |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 27.00% |
Minimum | Debt securities | United States |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 67.00% |
Minimum | Other | United States |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 0.00% |
Maximum | Equity securities | United States |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 33.00% |
Maximum | Debt securities | United States |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 73.00% |
Maximum | Other | United States |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Weighted average asset allocations | 3.00% |

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