Corporate restructuring (Details) $ in Millions		3 Months Ended	9 Months Ended
	Oct. 13, 2015 position	Oct. 30, 2015 USD ($)	Oct. 30, 2015 USD ($)
Corporate restructuring
Approximate number positions eliminated | position	255
Restructuring expenses		$ 6.1	$ 6.1
Remaining restructuring liability		$ 5.6	$ 5.6