CONDENSED CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Revenues:
Product sales	$ 757,918	$ 586,442	$ 2,119,253	$ 1,677,134
Product sales to related party	14,569	15,229	52,056	51,034
Commissions	5,961	4,772	15,670	14,237
Total revenues	778,448	606,443	2,186,979	1,742,405
Cost of product sales	680,973	528,932	1,909,356	1,513,286
Gross profit	97,475	77,511	277,623	229,119
Selling, general and administrative expenses	63,162	48,432	179,958	143,820
Depreciation and amortization	2,984	2,545	8,699	7,450
Operating income	31,329	26,534	88,966	77,849
Other income (expense):
Interest expense	(361)	(173)	(956)	(599)
Earnings of equity method investees	75	75	261	253
Other	195	154	548	567
Total other income (expense), net	(91)	56	(147)	221
Income before taxes	31,238	26,590	88,819	78,070
Income tax expense	(11,873)	(9,809)	(34,238)	(29,438)
Net income	$ 19,365	$ 16,781	$ 54,581	$ 48,632
Earnings Per Share, Basic and Diluted [Abstract]
Basic	$ 1.52	$ 1.32	$ 4.29	$ 3.84
Diluted	$ 1.52	$ 1.32	$ 4.28	$ 3.83
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]
Weighted Average Number of Shares Outstanding, Basic	12,718	12,679	12,712	12,672
Weighted Average Number of Shares Outstanding, Diluted	12,744	12,713	12,745	12,705