Shareholders' equity - Dividends (Details) - USD ($)	3 Months Ended						9 Months Ended
	Nov. 03, 2018	Aug. 04, 2018	May 05, 2018	Oct. 28, 2017	Jul. 29, 2017	Apr. 29, 2017	Nov. 03, 2018	Oct. 28, 2017
Dividends Payable [Line Items]
Dividends declared per share (usd per share)	$ 0.37	$ 0.37	$ 0.37	$ 0.31	$ 0.31	$ 0.31	$ 1.11	$ 0.93
Dividends, common stock	$ 19,200,000	$ 19,200,000	$ 21,800,000	$ 18,700,000	$ 18,700,000	$ 21,300,000	$ 60,200,000	$ 58,700,000
Cash dividends declared	0
Dividends on redeemable convertible preferred shares							24,600,000
Series A Redeemable Convertible Preferred Stock
Dividends Payable [Line Items]
Cash dividends declared	7,800,000	$ 7,800,000	$ 7,800,000	7,800,000	$ 7,800,000	$ 7,800,000	23,400,000	23,400,000
Dividends on redeemable convertible preferred shares	$ 400,000			$ 400,000			1,200,000	1,200,000
Accrued Expenses
Dividends Payable [Line Items]
Cash dividends declared							$ 7,800,000
Other Liabilities
Dividends Payable [Line Items]
Cash dividends declared								$ 7,800,000