Accounting Policies (Details 4) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014 item	Dec. 31, 2013	Dec. 31, 2012
Stock-based compensation
Number of stock-based compensation plans	1wts_NumberOfStockBasedCompensationPlans
Total unrecognized compensation costs related to unvested stock-based compensation arrangements	$ 20.2
Total weighted average remaining term of unrecognized compensation costs	1 year 10 months 24 days
Compensation cost recognized	8.6	9.6	6.6
Impact on both basic and diluted net income per common share for recognition of total stock-based compensation expense (in dollars per share)	$ 0.18	$ 0.14	$ 0.10
Cost of goods sold
Stock-based compensation
Compensation cost recognized	0.6
Selling, general and administrative expenses
Stock-based compensation
Compensation cost recognized	8.0
Stock options
Stock-based compensation
Tax benefit recorded for the compensation expense	0.7	1.2	0.7
Other Stock-based Plans
Stock-based compensation
Tax benefit recorded for the compensation expense	$ 1.6	$ 1.9	$ 1.4

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

-Paragraph 1

-Subparagraph (b)

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

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

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Represents the impact on both basic and diluted net income per common share for recognition of total stock-based compensation expense.

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