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Share Based Compensation Plans: Performance Share Plan (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Performance Share Award Payout, Shares of Common Stock Percentage | 100.00% |  |  |
Unrecognized compensation expense | $ 10.6 |  |  |
Performance Shares, Number of Shares Authorized |  |  |  | 35,571
Stock Issued During Period, Shares, Treasury Stock Reissued | 4,958 | 7,582 | 27,515 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Share-based Liabilities Paid | $ 0.3 | $ 0.5 | $ 1.6 |
Restricted Stock and RSUs, total fair value of shares vested | $ 0.7 | $ 1.0 | $ 3.3 |
Performance Shares |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Performance Share Award Payout, Cash Percentage | 50.00% |  |  |
Performance Share Award Payout, Shares of Common Stock Percentage | 50.00% |  |  |
Performance Share Award, Percentage of Target | 16.21% |  |  |
Blended volatility |  |  |  | 18.00%
Volatility Rate - Historic |  |  |  | 0.50
Volatility Rate - Implied |  |  |  | 0.50
Volatility range for the peer group, Maximum | 39.00% | 67.00% |  |
Target shares, value | $ 0.5 |  |  |
Performance Shares | Minimum |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Performance Share Award, Percentage of Target | 0.00% |  |  | 0.00%
Performance Shares | Maximum |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Performance Share Award, Percentage of Target | 200.00% |  |  | 200.00%
Performance Shares, Equity Awards |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Performance Shares, Number of Shares Authorized | 0 | 18,105 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ 0 | $ 81.42 |  |
Performance Shares, Granted in Period | 0 |  |  |
Weighted Average Grant Date Fair Value (usd per share) | $ 0 |  |  |
Shares Forfeited | 0 |  |  |
Forfeited (usd per share) | $ 0 |  |  |
Shares Vested | (18,105) |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value | $ 81.42 |  |  |
Performance Shares, Liability Awards |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Performance Shares, Number of Shares Authorized | 0 | 18,105 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ 0 |  |  |
Performance Shares, Granted in Period | 0 |  |  |
Shares Vested | (18,105) |  |  |

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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 718 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(01) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 + Details
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- Definition The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References No definition available. + Details
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