Stock-Based Compensation (Weighted-Average Assumptions Used in Estimating Grant Date Fair Values of Stock Option Awards) (Details) - Stock Options [Member] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Key assumptions used in estimating the grant date fair values of stock option awards granted
Total stock options granted	539,000	274,000	259,000
Weighted average grant date fair value	$ 13.11	$ 5.31	$ 12.48
Risk-free rate (as a percent)	1.81%	1.20%	1.30%
Expected life of options	4 years 9 months 18 days	4 years 2 months 12 days	4 years 8 months 12 days
Expected volatility (as a percent)	43.09%	40.60%	45.50%