CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Net sales	$ 5,327,205us-gaap_SalesRevenueNet	$ 5,085,293us-gaap_SalesRevenueNet	$ 5,080,106us-gaap_SalesRevenueNet
Cost of goods sold	4,516,704us-gaap_CostOfGoodsAndServicesSold	4,295,715us-gaap_CostOfGoodsAndServicesSold	4,305,502us-gaap_CostOfGoodsAndServicesSold
Gross profit	810,501us-gaap_GrossProfit	789,578us-gaap_GrossProfit	774,604us-gaap_GrossProfit
Operating expenses:
Warehousing, marketing and administrative expenses	592,050	580,428	573,693
Loss on sale of business	8,234us-gaap_GainLossOnSaleOfBusiness
Operating income	210,217us-gaap_OperatingIncomeLoss	209,150us-gaap_OperatingIncomeLoss	200,911us-gaap_OperatingIncomeLoss
Interest expense	16,234us-gaap_InterestExpense	12,233us-gaap_InterestExpense	23,619us-gaap_InterestExpense
Interest income	(500)us-gaap_InvestmentIncomeInterest	(593)us-gaap_InvestmentIncomeInterest	(343)us-gaap_InvestmentIncomeInterest
Income before income taxes	194,483	197,510	177,635
Income tax expense	75,285us-gaap_IncomeTaxExpenseBenefit	74,340us-gaap_IncomeTaxExpenseBenefit	65,805us-gaap_IncomeTaxExpenseBenefit
Net income	$ 119,198us-gaap_NetIncomeLoss	$ 123,170us-gaap_NetIncomeLoss	$ 111,830us-gaap_NetIncomeLoss
Net income per share - basic:
Net income per share - basic	$ 3.08us-gaap_EarningsPerShareBasic	$ 3.11us-gaap_EarningsPerShareBasic	$ 2.77us-gaap_EarningsPerShareBasic
Average number of common shares outstanding - basic	38,705	39,650	40,337
Net income per share - diluted:
Net income per share - diluted	$ 3.05us-gaap_EarningsPerShareDiluted	$ 3.06us-gaap_EarningsPerShareDiluted	$ 2.73us-gaap_EarningsPerShareDiluted
Average number of common shares outstanding - diluted	39,130	40,236	40,991

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 2

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.2(a),(d))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688