Compensation Plans: Stock Based (Details) $ / shares in Units, $ in Millions	12 Months Ended
	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