Summary of Significant Accounting Policies (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) stores states	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
Summary of significant accounting policies
Number of stores | stores	5,219
Number of states, in which the Company operates | states	47
Accounts receivable due from employees to the Company	$ 1,100	$ 900
Allowance for doubtful supplier receivables	0	0
Replacement cost of inventory	3,200,000	3,010,000
LIFO inventory value in excess of replacement cost of inventory	107,300	157,300
Goodwill impairment	0	0
Impairment of long-lived assets	11,400	0
Self-insurance reserves, current	77,012	71,695
Advertising expense, net	81,400	83,700	$ 83,000
Total interest costs capitalized	9,100	8,500	7,900
Deferred debt issuance costs, net of amortization	17,100	15,900
Original issuance discounts, net of accretion	4,300	3,700
Valuation allowance for deferred tax assets	0	$ 0
ASU 2016-02 [Member] | Forecast [Member]
Summary of significant accounting policies
Cumulative effective adjustment to opening Retained earnings				$ 1,400
Operating lease, right-of-use asset				1,900,000
Operating lease, liability				$ 2,000,000
Adoption of ASU 2014-09 (Topic 606) [Member]
Summary of significant accounting policies
Financial statement impact from adoption	0
Cumulative effective adjustment to opening Retained earnings	0
Adoption of ASU 2016-09 [Member]
Summary of significant accounting policies
Change in accounting policy, description		Upon adoption of ASU 2016-09, the Company elected to change its accounting policy to account for forfeitures as they occur; this change was applied using the modified retrospective transition method with a cumulative effect adjustment
Effect of accounting pronouncement adoption on Provision for income taxes	34,700	$ 48,700
Adoption of ASU 2016-09 [Member] | Reclassification or adjustment due to the adoption of an accounting pronouncement [Member]
Summary of significant accounting policies
Cumulative effective adjustment to opening Retained earnings		300
Tax withholdings for share-based compensation, reclassified from operating activities			600
Excess tax benefit from share-based compensation, reclassified from financing activities			$ 56,000
Adoption of ASU 2018-15 [Member]
Summary of significant accounting policies
Financial statement impact from adoption	0
Capitalized implementation costs	0
Other Assets [Member]
Summary of significant accounting policies
Deferred debt issuance costs, net of amortization	$ 1,500	$ 2,000
Loyalty Program Points [Member]
Summary of significant accounting policies
Deferred revenue, period expect to be recognized within	3 months
Loyalty Program Coupon [Member]
Summary of significant accounting policies
Deferred revenue, period expect to be recognized within	12 months