Stock-based Compensation: Incentive Award Plan and Employee Stock Purchase Plan Stock-based Compensation: Incentive Award Plan and Employee Stock Purchase Plan (RSU and RSAs) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	2,503,110
Award with service conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested RSUs and RSAs outstanding at January 1 (in shares)	465,369
Granted (in shares)	134,897
Vested (in shares)	(310,000)
Forfeited (in shares)	(11,004)
Unvested RSUs and RSAs outstanding at December 31 (in shares)	279,262	465,369
Unvested and expected to vest RSUs and RSAs outstanding at December 31 (in shares)	259,412
Awards with performance and service conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested RSUs and RSAs outstanding at January 1 (in shares)	881,251
Granted (in shares)	357,350
Vested (in shares)	(284,739)
Forfeited (in shares)	(37,269)
Unvested RSUs and RSAs outstanding at December 31 (in shares)	916,593	881,251
Unvested and expected to vest RSUs and RSAs outstanding at December 31 (in shares)	865,621
Restricted Stock Units and Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested RSUs and RSAs outstanding at January 1 (in shares)	1,346,620
Granted (in shares)	492,247
Vested (in shares)	(594,739)
Forfeited (in shares)	(48,273)
Unvested RSUs and RSAs outstanding at December 31 (in shares)	1,195,855	1,346,620
Unvested and expected to vest RSUs and RSAs outstanding at December 31 (in shares)	1,125,033
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Unvested RSUs and RSAs outstanding at January 1, weighted average grant date fair value (in dollars per share)	$ 36.31
Granted, weighted average grant date fair value (in dollars per share)	36.07	$ 40.49	$ 33.66
Vested, weighted average grant date fair value (in dollars per share)	$ 31.28
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures	38.42
Unvested RSUs and RSAs outstanding at December 31, weighted average grant date fair value (in dollars per share)	$ 38.78	$ 36.31
Unvested and expected to vest RSUs and RSAs outstanding at December 31, weighted average grant date fair value (in dollars per share)	$ 38.68