Stockholders' Equity (Schedule of 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
Stock-based compensation expense	$ 20,036	$ 15,420	$ 14,043
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation expense	0	444	974
Deferred Stock Unit
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation expense	10,696	7,830	7,023
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation expense	1,191	1,770	1,031
Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation expense	$ 8,149	$ 5,376	$ 5,015