Compensation Plans: Stock Based (Details) $ / shares in Units, $ in Millions		3 Months Ended		12 Months Ended
		Jun. 30, 2017 shares	Dec. 31, 2016 $ / shares shares	Dec. 31, 2017 USD ($) shares $ / shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options | $						$ 0.0
Number of shares available for grant				3,300,000
Impact outright issuance of one share has on number of available shares				1
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					0.2	1.0
Award Vesting Period				3 years
Stock-based compensation expense | $				$ 9.7	$ 11.0	$ 10.6
Unrecognized stock based compensation expense | $				$ 18.8
Multiplier assumed				1
Fair value of PSUs/RSUs Granted in Period | $				$ 15.5	$ 11.9	$ 14.5
Performance Share Units Shares Settled Gross of Shares for Tax Withholdings	[1]				44,870	288,962
Shares held for settlement of income and payroll tax obligations (in shares)					(14,809)	(100,683)
Shares Issued in Period					30,061	188,279
Fair value of PSUs/RSUs Vested in Period | $				$ 8.1	$ 8.4	$ 4.0
Weighted Average Grant Date Fair Value
Non-vested at beginning of year (in shares)	[2]			828,923	626,328	433,660
Granted (in shares)	[2]			977,731	447,971	320,753
Vested (in shares)	[2]			(94,338)	(130,353)	(76,438)
Forfeited (in shares)	[2]			(178,825)	(115,023)	(51,647)
Non-vested at end of year (in shares)	[2]		828,923	1,533,491	828,923	626,328
Non-vested outstanding at the beginning of the period (in dollars per share) | $ / shares	[2]			$ 43.25	$ 61.81	$ 73.63
Granted (in dollars per share) | $ / shares	[2]			15.86	26.56	45.34
Vested (in dollars per share) | $ / shares	[2]			85.85	64.17	51.76
Forfeited (in dollars per share) | $ / shares	[2]			44.99	55.59	73.62
Non-vested outstanding at the end of the period (in dollars per share) | $ / shares	[2]		$ 43.25	$ 22.97	$ 43.25	$ 61.81
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $				$ 10.3	$ 11.9	$ 13.4
Unrecognized stock based compensation expense | $				19.3
Fair value of PSUs/RSUs Granted in Period | $				$ 17.0	$ 11.7	$ 15.6
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting Increment				0.33	0.33	0.33
Shares held for settlement of income and payroll tax obligations (in shares)				(74,747)	(72,181)	(91,045)
Shares Issued in Period				171,278	169,182	187,244
Fair value of PSUs/RSUs Vested in Period | $				$ 10.8	$ 14.0	$ 17.6
Number of Shares Represented by Each RSU				1
Restricted Stock, Shares Settled Gross of Shares for Tax Withholdings	[3]			246,025	241,363	278,289
Weighted Average Grant Date Fair Value
Non-vested at beginning of year (in shares)				604,116	543,737	515,724
Granted (in shares)				1,020,780	417,065	356,246
Vested (in shares)				(246,025)	(241,363)	(278,289)
Forfeited (in shares)				(134,609)	(115,323)	(49,944)
Non-vested at end of year (in shares)			604,116	1,244,262	604,116	543,737
Non-vested outstanding at the beginning of the period (in dollars per share) | $ / shares				$ 37.39	$ 55.01	$ 68.29
Granted (in dollars per share) | $ / shares				16.64	28.08	43.72
Vested (in dollars per share) | $ / shares				43.99	58.06	63.12
Forfeited (in dollars per share) | $ / shares				26.38	43.52	66.53
Non-vested outstanding at the end of the period (in dollars per share) | $ / shares			$ 37.39	$ 20.25	$ 37.39	$ 55.01
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	$ 2.0	$ 1.6
Director Shares
Minimum Service Requirement for Immediate Vesting of Granted Shares				5 years
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
Director [Member]
Director Shares
Stock Issued During Period, Shares, Share-based Compensation, Gross		71,573	53,473			39,903
Director [Member] | Restricted Stock Units (RSUs) [Member]
Weighted Average Grant Date Fair Value
Granted (in shares)		8,794

[1] During the years ended December 31, 2016, and 2015, the Company issued shares of common stock for PSUs granted in 2013, and 2012. The Company and a majority of grant recipients mutually agreed to net share settle a portion of the awards to cover income and payroll tax withholdings in accordance with the Company’s Equity Plan and individual award agreements.

[2] 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.

[3] During the years ended December 31, 2017, 2016, and 2015, the Company issued shares of common stock for RSUs granted in previous years. The Company and a majority of grant recipients mutually agreed to net share settle a portion of the awards to cover income and payroll tax withholdings in accordance with the Company’s Equity Plan and individual award agreements.