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Stock based compensation plans (Details) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) yr shares	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Share-based Compensation [Abstract]
Share-based compensation arrangement, number of shares available for grant | shares	5.6
Share-based compensation expense, net of tax	$ 2.9	$ 4.4	$ 3.9
Share-based compensation nonvested awards total compensation cost not yet recognized	$ 5.6
Share-based compensation, nonvested awards, total compensation cost not yet recognized, period for recognition | yr	1.5

X

- Definition

As of the balance sheet date, the aggregate unrecognized cost of equity-based awards under equity-based compensation awards that have yet to vest.

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	instant

X

- Definition

The weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, using a decimal to express in number of years.

+ References

No definition available.

+ Details

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Period Type:	instant

X

- Definition

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.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- References

No definition available.

+ Details

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X

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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