Stock-based Compensation: Incentive Award Plan and Employee Stock Purchase Plan Stock-based Compensation: Incentive Award Plan and Employee Stock Purchase Plan (Stock Options Activity) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Outstanding Stock Options Activity [Roll Forward]
Outstanding at December 31 (in shares)	169,919
Exercisable at December 31 (in shares)	169,919
Options Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding - weighted average exercise price per share	$ 12.11
Exercised, weighted average exercise price per share	12.14
Canceled, weighted average exercise price per share	8.10
Vested and Expected to Vest, weighted average exercise price per share	12.10
Exercisable, weighted average exercise price per share	$ 12.10
Outstanding, weighted average remaining contractual term	4 years 3 months	3 years 6 months
Vested and Expected to Vest, weighted average remaining contractual term	4 years 3 months
Exercisable, weighted average remaining contractual term	4 years 3 months
Options outstanding - aggregate intrinsic value	$ 5,448,000	$ 11,705,000
Vested and Expected to Vest, aggregate intrinsic value	5,448,000
Exercisable, aggregate intrinsic value	5,448,000
Employee Stock Option [Member]
Options Outstanding, Weighted Average Exercise Price [Roll Forward]
Total intrinsic value of options exercised	$ 4,700,000	$ 10,900,000	$ 3,900,000
Non Qualified Stock Options [Member]
Outstanding Stock Options Activity [Roll Forward]
Outstanding at January 1 (in shares)	356,386
Exercised (in shares)	(185,484)
Canceled (in shares)	(983)
Outstanding at December 31 (in shares)	169,919	356,386
Vested and Expected to Vest at December 31(in shares)	169,919
Exercisable at December 31 (in shares)	169,919