Share-Based Awards - Summary of Compensation Costs (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based expense	$ 4.9	$ 4.2	$ 5.4
Total recognized tax benefit	(1.5)	(1.3)	(1.8)
Share-based expense (net of tax)	3.4	2.9	3.6
Cash received upon option exercise	4.5	7.6	20.9
Intrinsic value of options exercised	5.4	6.7	13.4
Tax benefit realized upon option exercise	2.0	2.5	2.3
Fair value of stock vested	2.6	5.2	4.2
Stock Options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based expense	0.3	0.7	1.1
Incremental non cash share based compensation expense
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based expense	0.2	0.5	1.2
Restricted Stock Units (RSUs)
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based expense	$ 4.4	$ 3.0	$ 3.1

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

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The amount of expense, net of income tax, 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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Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

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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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Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

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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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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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