CONDENSED CONSOLIDATED STATEMENTS OF INCOME (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]
Net sales	$ 1,419,947	$ 1,336,676	$ 3,994,123	$ 3,861,655
Cost of goods sold	1,208,919	1,133,015	3,396,552	3,267,533
Gross profit	211,028	203,661	597,571	594,122
Operating expenses:
Warehousing, marketing and administrative expenses	146,560	136,265	437,595	442,558
Operating income	64,468	67,396	159,976	151,564
Interest expense, net	3,992	2,734	11,199	8,703
Income before income taxes	60,476	64,662	148,777	142,861
Income tax expense	22,307	24,161	55,420	53,816
Net income	$ 38,169	$ 40,501	$ 93,357	$ 89,045
Net income per share - basic:
Net income per share - basic	$ 0.99	$ 1.03	$ 2.41	$ 2.24
Average number of common shares outstanding - basic	38,450	39,468	38,817	39,732
Net income per share - diluted:
Net income per share - diluted	$ 0.98	$ 1.01	$ 2.38	$ 2.21
Average number of common shares outstanding - diluted	38,884	40,031	39,244	40,331
Dividends declared per share	$ 0.14	$ 0.14	$ 0.42	$ 0.42