Shareholders' equity - Share Repurchase (Details) - USD ($)	3 Months Ended
	Apr. 30, 2016	May. 02, 2015	Jun. 14, 2013
2013 Program
Class of Stock [Line Items]
Amount authorized			$ 350,000,000
Shares repurchased (shares)	1,121,543	160,298
Amount repurchased	$ 125,000,000	$ 21,900,000
Average repurchase price per share (usd per share)	$ 111.45	$ 136.84
Remaining authorized repurchase amount	$ 10,600,000
Other current liabilities
Class of Stock [Line Items]
Shares repurchased but not yet settled and paid		$ 2,800,000
Accrued expenses
Class of Stock [Line Items]
Shares repurchased but not yet settled and paid		$ 2,800,000