Current and long-term obligations (Details) (USD $)	9 Months Ended	0 Months Ended	9 Months Ended						9 Months Ended
	Nov. 01, 2013	Apr. 11, 2013 Senior unsecured credit facilities, maturity April 11, 2018	Oct. 31, 2014 Senior unsecured credit facility, maturity April 11, 2018, Term Facility	Apr. 11, 2013 Senior unsecured credit facility, maturity April 11, 2018, Term Facility	Oct. 31, 2014 Senior unsecured credit facility, maturity April 11, 2018, Revolving Facility	Apr. 11, 2013 Senior unsecured credit facility, maturity April 11, 2018, Revolving Facility	Oct. 31, 2014 Senior unsecured credit facility, maturity April 11, 2018, Revolving Facility Letters of credit	Apr. 11, 2013 Senior unsecured credit facility, maturity April 11, 2018, Revolving Facility Letters of credit	Nov. 01, 2013 Previous Senior Secured Credit Facilities	Apr. 11, 2013 1.875% Senior Notes due April 15, 2018	Apr. 11, 2013 3.25% Senior Notes due April 15, 2023	Apr. 11, 2013 2018 and 2023 Senior Notes	Oct. 31, 2014 Letter of Credit Outside of Revolving Facility
Current and long-term obligations
Credit agreement term		5 years
Maximum financing under credit agreements						$ 850,000,000		$ 250,000,000
Discount on debt issuance										500,000	2,400,000
Debt issue cost capitalized		5,900,000										10,100,000
Amount borrowed				1,000,000,000						400,000,000	900,000,000
Stated interest rate (as a percent)										1.875%	3.25%
Amount of quarterly installments beginning August 1, 2014			25,000,000
Amount of outstanding borrowings			950,000,000
Amount of outstanding borrowings					0
Letters of credit outstanding							31,200,000						21,300,000
Borrowing availability under credit facility					818,800,000
Loss on debt retirement, net	$ 18,871,000								$ 18,900,000