Stock-Based Compensation (Narrative) (Details) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($) plan $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based compensation plans \| plan	1
Number of shares authorized \| shares	13,118,430
Capitalization of stock based compensation expense	$ 0.0
Proceeds from stock options exercised	$ 4.2	$ 6.8	$ 0.7
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number \| shares	4,272,651	4,133,874
Exercise period	7 years
Award vesting period	3 years
Proceeds from stock options exercised	$ 4.2	$ 6.8	0.7
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	2.8	3.5	0.7
Fair value of options vested during the period	2.6	$ 4.1	3.8
Unrecognized compensation expense	$ 2.7
Weighted average years expense to be recognized over	1 year 5 months 24 days
Stock-settled stock appreciation rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number \| shares		0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value		$ 2.9	$ 2.0
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 4.6
Weighted average years expense to be recognized over	1 year 10 months 5 days
Shares outstanding \| shares	1,534,058	1,910,669
Weighted average grant date fair value \| $ / shares	$ 12.65	$ 8.05	$ 7.58
Fair value of stock awards vested	$ 5.5	$ 5.2	$ 10.3
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 11.2
Weighted average years expense to be recognized over	1 year 8 months 4 days
Shares outstanding \| shares	3,531,312	4,281,792
Weighted average grant date fair value \| $ / shares	$ 12.75	$ 7.65	$ 7.52
Fair value of stock awards vested	$ 9.3	$ 8.1	$ 5.4
Share-based Compensation, Equity Instruments Other than Options, Shares Called upon Vested \| shares	1
Minimum \| RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Minimum \| PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Percentage awarded	0.00%
Maximum \| PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage awarded	150.00%
Fully Vested On The Grant Date \| RSUs \| Non-employee directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense, shares that vests on grant date	$ 0.8	$ 0.9	$ 0.8

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