Stock-Based Compensation (Employee Stock Purchase Plan) (Details) - Employee Stock Purchase Plan - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 850	$ 1,205	$ 921
Common stock shares purchased by Company employees (in shares)	446,490	394,120	355,557
Average purchase price per share (in USD per share)	$ 5.64	$ 8.17	$ 8.33