Stock-Based Compensation and Directors Stock Purchase Plan Stock-Based Compensation and Directors Stock Purchase Plan (Additional Information About Stock Options and SARs Exercises) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation [Abstract]
Intrinsic value of options and SARs exercised	$ 9,632	$ 9,310	$ 8,854
Tax benefit realized from options and SARs exercised	$ 1,928	$ 2,698	$ 1,781