Derivatives and hedging activities (Details) (USD $) In Millions, unless otherwise specified	Oct. 31, 2014
Cash flow hedges of interest rate risk
Estimated amount to be reclassified during the next 52 week period	$ 3.5
Interest rate swaps \| Cash flow hedge
Cash flow hedges of interest rate risk
Combined notional value	$ 875.0

Nominal or face amount used to calculate payments on the derivative liability.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5580258-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5579245-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

-URI http://asc.fasb.org/extlink&oid=6519104

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Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant