Summary of Significant Accounting Policies (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) stores states	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Summary of significant accounting policies
Number of stores | stores	4,829
Number of states, in which the Company operates | states	47
Accounts receivable due from employees to the Company	$ 1,200	$ 1,100
Allowance for doubtful supplier receivables	0	0
Replacement cost of inventory	2,780,000	2,630,000
LIFO inventory value in excess of replacement cost of inventory	132,000	85,900
Notes receivable from suppliers and other third parties		17,300
Reserve for uncollectable notes receivables		0
Goodwill impairment	0	0
Impairment of long-lived assets	0	0
Self-insurance reserves, current	67,921	72,741
Advertising expense, net	83,000	79,300	$ 79,000
Total interest costs capitalized	7,900	7,400	$ 11,500
Deferred debt issuance costs, net of amortization	10,600	8,300
Original issuance discounts, net of accretion	3,100	2,900
Valuation allowance for deferred tax assets	0	0
Other assets, net [Member]
Summary of significant accounting policies
Deferred debt issuance costs, net of amortization	700	1,200
Loyalty program [Member]
Summary of significant accounting policies
Deferred revenue, loyalty program	4,800	7,200
Deferred revenue recognized, loyalty program	$ 12,700	$ 11,200