Share-Based Compensation Plans (Stock Options) (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Shares Outstanding beginning balance | shares	2,443
Number of Shares Granted | shares	2,900
Number of Shares Exercised | shares	(469)
Number of Shares Forfeited or expired | shares	(122)
Number of Shares Outstanding ending balance | shares	4,752
Number of Shares Fully vested and expected to vest | shares	4,632
Number of Shares Exercisable | shares	1,733
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted Average Exercise Price Per Share Outstanding beginning balance (in dollars per share) | $ / shares	$ 6.93
Weighted Average Exercise Price Per Share Granted (in dollars per share) | $ / shares	9.97
Weighted Average Exercise Price Per Share Exercised (in dollars per share) | $ / shares	6.66
Weighted Average Exercise Price Per Share Forfeited or expired (in dollars per share) | $ / shares	5.12
Weighted Average Exercise Price Per Share Outstanding ending balance (in dollars per share) | $ / shares	8.86
Weighted Average Exercise Price Per Share Fully vested and expected to vest (in dollars per share) | $ / shares	8.83
Weighted Average Exercise Price Per Share Exercisable (in dollars per share) | $ / shares	$ 7.17
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contractual Term Outstanding (years)	7 years 6 months 3 days
Average Remaining Contractual Term Fully vested and expected to vest (years)	7 years 5 months 16 days
Average Remaining Contractual Term Exercisable (years)	4 years 9 months
Aggregate intrinsic value Outstanding ending balance (in dollars) | $	$ 6,403
Aggregate intrinsic value Fully vested and expected to vest (in dollars) | $	6,369
Aggregate intrinsic value Exercisable (in dollars) | $	$ 5,455