Earnings per Share (Schedule of Earnings per Share, Basic and Diluted) (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Weighted average common shares outstanding, used in computing basic earnings per share	69,759	69,683	70,162
Effect of dilutive stock options and restricted stock units	694	949	902
Weighted-average common shares outstanding, used in computing diluted earnings per share	70,453	70,632	71,064
Basic	$ 1.51	$ 2.75	$ 2.48
Diluted	$ 1.49	$ 2.72	$ 2.45