Related party transactions (Details) (USD $)	6 Months Ended			6 Months Ended		1 Months Ended		6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended
	Aug. 02, 2013	Aug. 03, 2012	Aug. 02, 2013 Affiliates of KKR and Goldman, Sachs & Co. Maximum	Aug. 02, 2013 Affiliates of KKR and Goldman, Sachs & Co. Credit facilities	Aug. 03, 2012 Affiliates of KKR and Goldman, Sachs & Co. Credit facilities	May 03, 2013 Goldman, Sachs & Co. and affiliates Senior unsecured credit facilities	May 03, 2013 Goldman, Sachs & Co. and affiliates Senior notes	Aug. 03, 2012 Goldman, Sachs & Co. and affiliates Senior notes	Apr. 06, 2012 Goldman, Sachs & Co. and affiliates Previous Senior Secured Credit Facilities	Aug. 02, 2013 KKR person	May 03, 2013 KKR Senior notes	Aug. 03, 2012 KKR Senior notes	Apr. 06, 2012 KKR Previous Senior Secured Credit Facilities
Related party transactions
Ownership interest (as a percent)			5.00%
Number of members serving on the entity's board of directors										2
Interest paid				$ 17,100,000	$ 34,700,000
Payment of underwriting fees	$ 15,996,000	$ 15,067,000				$ 700,000	$ 1,500,000	$ 1,200,000	$ 500,000		$ 700,000	$ 1,200,000	$ 400,000