Stockholders' Equity (Schedule of Exercise of Stock Options) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stockholders' Equity Note [Abstract]
Intrinsic value of stock options exercised	$ 2,340	$ 13,204	$ 9,424
Cash receipts from stock options exercised	450	2,772	3,280
Income tax benefits from stock option exercises	900	4,435	2,885
Grant date fair value of stock options vested	$ 0	$ 506	$ 1,055