Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized under stock compensation plan	7.8
Shares available for grant under stock compensation plan	4.9
Share-based compensation expense	$ 7.6	$ 4.6	$ 4.8
Tax benefit from share-based compensation expense	$ 1.8	$ 1.1	$ 2.2
Vesting period	3 years
Weighted average fair value of options granted (usd per share)	$ 7.17	$ 7.00	$ 4.25
Stock options, vested and expected to vest, outstanding (shares)	2.3
Stock options, vested and expected to vest, weighted average exercise price (usd per share)	$ 12.29
Exercisable at end of year (shares)	1.8	1.6	1.6
Stock options, expected to vest (shares)	0.5
Stock options outstanding, aggregate intrinsic value	$ 18.2
Stock options exercisable, aggregate intrinsic value	16.4
Stock options exercised during the period, total intrinsic value	3.0	$ 2.3	$ 0.4
Tax benefit from stock options exercised	0.8	0.9	0.1
Proceeds from stock compensation activity	1.3	1.6	0.5
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense related to share-based compensation plans	2.1	2.2	2.1
Unrecognized compensation cost	$ 2.1
Weighted-average recognition period for unrecognized compensation cost	1 year 9 months 18 days
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense related to share-based compensation plans	$ 1.8	1.6	1.2
Unrecognized compensation cost	$ 1.7
Weighted-average recognition period for unrecognized compensation cost	1 year 10 months 25 days
Grant-date fair value of awards vested	$ 1.0	1.5	1.3
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense related to share-based compensation plans	3.7	0.8	1.5
Unrecognized compensation cost, performance share units	$ 4.5
Weighted-average recognition period for unrecognized compensation cost	1 year 8 months 12 days
Grant-date fair value of awards vested	$ 1.7	$ 0.3	$ 3.7
Minimum \| PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	0.00%
Maximum \| PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	200.00%
Performance-based Restricted Stock Units, 2016 Grants \| PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Performance share units performance period	3 years
Vesting percentage	98.00%
Performance-based Restricted Stock Units, 2017 Grants \| PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Performance share units performance period	3 years
Performance-based Restricted Stock Units, 2018 Grants \| PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Performance share units performance period	3 years

Share Based Compensation Arrangement by Share Based Payment Award, Performance Period

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Share-based Compensation Arrangement by Share-based Payment Award, Options, Expected to Vest, Outstanding, Number

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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Unrecognized cost of unvested options awarded to employees as compensation.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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Amount of cash inflow from issuance of shares under share-based compensation arrangement. Issuance includes, but is not limited to, exercise of stock options and similar instruments.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Percentage of vesting of share-based compensation awards.

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Amount of capitalized and expensed compensation cost from equity-based compensation arrangements.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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