Share-based compensation plans - Narrative (Details) $ in Millions		3 Months Ended
Jul. 11, 2014 employees	Jun. 30, 2014 USD ($)
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of employees impacted by policy revision \| employees	130
Expense from recoupment policy change		$ 4.2

An excess of the fair value of the modified award over the fair value of the award immediately before the modification.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)(iii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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