Stock-Based Compensation (Stock Option and SSARs Activity) (Details) - Stock options $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Number Outstanding [Roll Forward]
Outstanding at December 31, 2016 | shares	4,133,874
Granted | shares	745,772
Exercised | shares	(547,107)
Forfeited | shares	(59,888)
Outstanding at December 31, 2017 | shares	4,272,651
Weighted Average Exercise Price [Roll Forward]
Outstanding at December 31, 2016 | $ / shares	$ 7.82
Granted | $ / shares	12.75
Exercised | $ / shares	7.72
Forfeited | $ / shares	9.57
Outstanding at December 31, 2017 | $ / shares	$ 8.68
Outstanding at December 31, 2017, Weighted Average Remaining Contractual Term	3 years 4 months 3 days
Outstanding at December 31, 2017, Aggregate Intrinsic Value | $	$ 15.5
Exercisable shares at December 31, 2017 | shares	3,157,606
Exercisable shares at December 31, 2017, Weighted Average Exercise Price | $ / shares	$ 7.88
Exercisable shares at December 31, 2017, Weighted Average Contractual Term	2 years 7 months 3 days
Exercisable shares at December 31, 2017, Aggregate Intrinsic Value | $	$ 13.6