Compensation Plans: Stock Based (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) shares $ / shares	Dec. 31, 2022 USD ($) shares $ / shares	Dec. 31, 2021 USD ($) shares $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant	2,800,000
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		2.0	1.0
Stock-based compensation expense | $	$ 2.8	$ 2.6	$ 6.0
Unrecognized stock based compensation expense | $	8.6
Fair value of PSUs/RSUs granted in period | $	$ 7.7	$ 7.4
Award vesting period	3 years
Non-vested at beginning of year (in shares)	273,258	464,483	830,464
Non-vested outstanding at beginning of year grant date fair value ($/share) | $ / shares	$ 26.67	$ 12.80	$ 17.52
Granted (in shares)	256,633	276,010	0
Granted grant date fair value ($/share) | $ / shares	$ 29.93	$ 26.67	$ 0
Vested (in shares)	(15,950)	(461,387)	(352,395)
Vested grant date fair value ($/share) | $ / shares	$ 25.50	$ 12.81	$ 23.81
Forfeited (in shares)	(44,509)	(5,848)	(13,586)
Forfeited grant date fair value ($/share) | $ / shares	$ 26.45	$ 18.24	$ 15.46
Non-vested at end of year (in shares)	469,432	273,258	464,483
Non-vested outstanding at end of year grant date fair value ($/share) | $ / shares	$ 27.83	$ 26.67	$ 12.80
Performance share units, shares settled gross of shares for tax withholdings		1,004,410	347,742
Shares held for settlement of income and payroll tax obligations (in shares)		(349,487)	(112,919)
Shares Issued in Period	0	654,923	234,823
Fair value of PSUs/RSUs Vested in Period | $		$ 12.3	$ 8.4
Multiplier assumed	1	1	1
Performance Shares (PSUs) | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplier applied to PSU awards at settlement	0
Performance Shares (PSUs) | Maximum
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 | $	$ 14.8	$ 13.5	$ 10.2
Unrecognized stock based compensation expense | $	25.7
Fair value of PSUs/RSUs granted in period | $	$ 20.2	$ 18.0	$ 17.0
Non-vested at beginning of year (in shares)	1,375,052	1,841,237	2,097,860
Non-vested outstanding at beginning of year grant date fair value ($/share) | $ / shares	$ 22.42	$ 13.79	$ 8.83
Granted (in shares)	630,474	526,776	666,052
Granted grant date fair value ($/share) | $ / shares	$ 32.03	$ 34.08	$ 25.52
Vested (in shares)	(805,205)	(920,927)	(843,098)
Vested grant date fair value ($/share) | $ / shares	$ 16.75	$ 12.17	$ 11.00
Forfeited (in shares)	(119,777)	(72,034)	(79,577)
Forfeited grant date fair value ($/share) | $ / shares	$ 29.26	$ 18.24	$ 10.64
Non-vested at end of year (in shares)	1,080,544	1,375,052	1,841,237
Non-vested outstanding at end of year grant date fair value ($/share) | $ / shares	$ 31.49	$ 22.42	$ 13.79
Performance share units, shares settled gross of shares for tax withholdings	803,449	920,927	843,098
Shares held for settlement of income and payroll tax obligations (in shares)	(249,233)	(284,423)	(250,349)
Shares Issued in Period	554,216	636,504	592,749
Number of Shares Represented by Each RSU	1
Fair value of PSUs/RSUs Vested in Period | $	$ 13.5	$ 11.2	$ 9.3