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Common Stock and Earnings Per Share - Summary of Common Stock (Details) - USD ($) shares in Thousands, $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Summary of Common Stock [Line Items] |  |  |  |
Balance, Shares | 53,200 | 52,100 |  |
Common Stock [Member] |  |  |  |
Summary of Common Stock [Line Items] |  |  |  |
Balance, Shares | 53,220 | 52,085 | 51,679 | 51,509
Balance, Equity | $ 1,536.7 | $ 1,460.9 | $ 1,436.7 | $ 1,428.5
Employee Stock Purchase Plan, Shares | 17 | 13 | 8 |
Employee Stock Purchase Plan, Equity | $ 0.8 | $ 0.7 | $ 0.7 |
Invest Direct, Shares | 263 | 309 | 38 |
Invest Direct, Equity | $ 17.5 | $ 18.3 | $ 3.0 |
Options and Stock Awards, Shares | 49 | 35 | 85 |
Options and Stock Awards, Equity | $ 3.4 | $ 2.2 | $ 1.3 |
Contributions to RSOP, Shares | 24 | 49 | 39 |
Contributions to RSOP, Equity | $ 3.1 | $ 3.0 | $ 3.2 |
Common Stock Issued | $ 51.0 |  |  |
Equity Issuance Program, Shares | 782 | 0 | 0 |
Equity Issuance Program Shares Authorized |  |  | 13,600 |
Equity Issuance Program Shares Available for Issuance | 2,100 |  |  |
Common Stock [Member] | PIE Shares |  |  |  |
Summary of Common Stock [Line Items] |  |  |  |
Equity Issuance Program, Shares | 800 |  |  |

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