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Compensation Plans: Stock Based (Details) $ / shares in Units, $ in Millions | 12 Months Ended
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Dec. 31, 2020 USD ($) shares $ / shares | Dec. 31, 2019 USD ($) $ / shares shares | Dec. 31, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Shares available for grant | 3,800,000 |  |
Impact outright issuance of one share has on number of available shares | 1 |  |
Performance Shares (PSUs) |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Maximum impact of issuance of one performance share award on available shares under the equity incentive plan | 2 |  |
Multiplier applied to PSU awards at settlement | 0.9 | 0 | 0
Award vesting period | 3 years |  |
Retirement vesting Increment | 6 months |  |
Retirement increment vesting period | 6 months |  |
TSR multiplier cap | 1 |  |
Stock-based compensation expense | $ | $ 4.4 | $ 10.9 | $ 10.3
Unrecognized stock based compensation expense | $ | $ 4.4 |  |
Non-vested at beginning of year (in shares) | 2,022,585 | 1,711,259 | 1,533,491
Non-vested outstanding at the beginning of the period (in dollars per share) | $ / shares | $ 16.87 | $ 20.68 | $ 22.97
Granted (in shares) | 0 | 793,125 | 572,924
Granted (in dollars per share) | $ / shares | $ 0 | $ 12.80 | $ 24.45
Vested (in shares) | (792,572) | (346,021) | (233,102)
Vested (in dollars per share) | $ / shares | $ 15.85 | $ 26.32 | $ 44.25
Forfeited (in shares) | (399,549) | (135,778) | (162,054)
Forfeited (in dollars per share) | $ / shares | $ 17.56 | $ 16.98 | $ 21.79
Non-vested at end of year (in shares) | 830,464 | 2,022,585 | 1,711,259
Non-vested outstanding at the end of the period (in dollars per share) | $ / shares | $ 17.52 | $ 16.87 | $ 20.68
Multiplier assumed | 1 |  |
Fair value of PSUs/RSUs granted in period | $ |  | $ 10.2 | $ 14.0
Shares held for settlement of income and payroll tax obligations (in shares) | 215,451 |  |
Shares Issued in Period | 485,060 | 0 | 0
Fair value of PSUs/RSUs Vested in Period | $ | $ 12.6 | $ 9.1 | $ 10.3
Performance Shares (PSUs) | Minimum [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Multiplier applied to PSU awards at settlement | 0 |  |
Performance Shares (PSUs) | Maximum [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Multiplier applied to PSU awards at settlement | 2 |  |
Restricted Stock Units (RSUs) |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Retirement vesting Increment | 6 months |  |
Retirement increment vesting period | 6 months |  |
Stock-based compensation expense | $ | $ 8.7 | $ 11.1 | $ 10.8
Unrecognized stock based compensation expense | $ | $ 14.7 |  |
Non-vested at beginning of year (in shares) | 1,532,131 | 1,243,163 | 1,244,262
Non-vested outstanding at the beginning of the period (in dollars per share) | $ / shares | $ 16.01 | $ 21.50 | $ 20.25
Granted (in shares) | 1,458,869 | 978,932 | 583,552
Granted (in dollars per share) | $ / shares | $ 5.98 | $ 12.36 | $ 25.77
Vested (in shares) | (746,132) | (466,535) | (407,529)
Vested (in dollars per share) | $ / shares | $ 16.74 | $ 21.94 | $ 24.30
Forfeited (in shares) | (147,008) | (223,429) | (177,122)
Forfeited (in dollars per share) | $ / shares | $ 15.34 | $ 18.16 | $ 17.26
Non-vested at end of year (in shares) | 2,097,860 | 1,532,131 | 1,243,163
Non-vested outstanding at the end of the period (in dollars per share) | $ / shares | $ 8.83 | $ 16.01 | $ 21.50
Fair value of PSUs/RSUs granted in period | $ | $ 8.7 | $ 12.1 | $ 15.0
Shares held for settlement of income and payroll tax obligations (in shares) | 209,173 | 132,136 | 115,784
Shares Issued in Period | 536,959 | 334,399 | 291,745
Fair value of PSUs/RSUs Vested in Period | $ | $ 12.5 | $ 10.2 | $ 9.9
Number of Shares Represented by Each RSU | 1 |  |
Restricted Stock, Shares Settled Gross of Shares for Tax Withholdings | 746,132 | 466,535 | 407,529

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