Related Parties (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 bulk_facilities stores	Dec. 31, 2013	Dec. 31, 2012
Related Party Transaction
Number of stores	4,366
Related parties [Member]
Related Party Transaction
Number of stores	77
Number of bulk facilities	1
Lease payments under related party operating leases	$ 4.6	$ 4.4	$ 4.4