Stock Based Compensation Stock Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	3,900,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,504,487
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	$ 9,273	$ 142	$ 700
Allocated Share-based Compensation Expense	3,700	$ 3,300	$ 3,200
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 6,900
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	1 year 355 days
Stock Units Awarded Under the 2009 LTIP Plan	18,000	15,000	15,000
Value of Stock Units Awarded Under the 2009 LTIP Plan	$ 500	$ 300	$ 300
Total Numbner of Units Outstanding Under the 2006 Director Equity Plan	8,059
Value of Units Outstanding Under the 2006 Director Equity Plan	$ 200
Deferred Compensation Liability, Current and Noncurrent	400	100	300
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	3,250	5,482
Stock or Unit Option Plan Expense	$ (217)	$ (227)	$ (21)
Total Stock Units Outstanding Under All Stock Option Plans	51,787
Total Value of Units Outstanding Under All Stock Option Plans	$ 1,200
Deferred Compensation Equity	2,400
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits	$ 1,300