Compensation Plans: Stock Based (Details) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2015 USD ($) shares $ / shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant		2,800,000
Impact outright issuance of one share has on number of available shares		1
Director Shares
Minimum Service Requirement for Immediate Vesting of Granted Shares		5 years
Shares Issued to the Board of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Period		1 year
Stock-based compensation expense | $		$ 1.6	$ 1.6	$ 1.4
Director Shares
Stock Issued During Period, Shares, Share-based Compensation, Gross		37,950	27,677	28,169
Shares Issued to Former CEO for Service As Director [Member]
Director Shares
Stock Issued During Period, Shares, Share-based Compensation, Gross		1,953
Performance Shares [Member]
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		1.0	0.55	1.725
Award Vesting Period		3 years
Stock-based compensation expense | $		$ 10.6	$ 16.0	$ 16.8
Unrecognized stock based compensation expense | $		18.4
Fair value of PSUs/RSUs Granted in Period | $		$ 14.5	19.2	17.6
Multiplier assumed		1
Fair value of PSUs/RSUs Vested in Period | $		$ 4.0	$ 13.4	$ 20.7
Shares Issued in Period		188,279	85,121	387,461
Shares held for settlement of income and payroll tax obligations (in shares)		100,683	45,042	200,050
Weighted Average Grant Date Fair Value
Non-vested at beginning of year (in shares)	[1]	433,660	572,469	669,308
Granted (in shares)	[1]	320,753	202,404	274,831
Vested (in shares)	[1]	(76,438)	(206,830)	(345,005)
Forfeited (in shares)	[1]	(51,647)	(134,383)	(26,665)
Non-vested at end of year (in shares)	[1]	626,328	433,660	572,469
Non-vested outstanding at the beginning of the period (in dollars per share) | $ / shares	[1]	$ 73.63	$ 66.07	$ 63.91
Granted (in dollars per share) | $ / shares	[1]	45.34	94.66	64.13
Vested (in dollars per share) | $ / shares	[1]	51.76	64.79	60.06
Forfeited (in dollars per share) | $ / shares	[1]	73.62	86.72	69.74
Non-vested outstanding at the end of the period (in dollars per share) | $ / shares	[1]	$ 61.81	$ 73.63	$ 66.07
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Period		3 years
Stock-based compensation expense | $		$ 13.4	$ 13.9	$ 13.1
Unrecognized stock based compensation expense | $		19.3
Fair value of PSUs/RSUs Granted in Period | $		$ 15.6	$ 19.7	$ 19.8
PSU/RSU Vesting Increment		0.33	0.33	0.33
Fair value of PSUs/RSUs Vested in Period | $		$ 17.6	$ 14.7	$ 10.3
Restricted Stock, Shares Settled Gross of Shares for Tax Withholdings		278,289	253,031	207,378
Shares held for settlement of income and payroll tax obligations (in shares)		91,045	81,434	67,987
Number of Shares Represented by Each RSU		1
Restricted Stock, Shares Issued Net of Shares for Tax Withholdings		187,244	171,597	139,391
Weighted Average Grant Date Fair Value
Non-vested at beginning of year (in shares)		515,724	580,431	496,244
Granted (in shares)		356,246	234,560	329,939
Vested (in shares)		(278,289)	(253,031)	(207,376)
Forfeited (in shares)		(49,944)	(46,236)	(38,376)
Non-vested at end of year (in shares)		543,737	515,724	580,431
Non-vested outstanding at the beginning of the period (in dollars per share) | $ / shares		$ 68.29	$ 57.05	$ 51.81
Granted (in dollars per share) | $ / shares		43.72	83.98	60.01
Vested (in dollars per share) | $ / shares		63.12	58.19	49.73
Forfeited (in dollars per share) | $ / shares		66.53	62.06	54.37
Non-vested outstanding at the end of the period (in dollars per share) | $ / shares		$ 55.01	$ 68.29	$ 57.05
Minimum [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplier Applied to PSU Awards at Settlement		0
Maximum [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplier Applied to PSU Awards at Settlement		2

[1] The number of awards assumes a multiplier of one. The final number of shares of common stock issued may vary depending on the three-year performance multiplier, which ranges from zero to two.