CONDENSED CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Revenues:
Product sales	$ 2,260,279	$ 1,996,294	$ 1,489,500
Product sales to related party	68,355	61,873	55,185
Commissions	18,851	16,979	20,655
Total revenues	2,347,485	2,075,146	1,565,340
Cost of product sales	2,043,147	1,808,230	1,359,755
Gross profit	304,338	266,916	205,585
Selling, general and administrative expenses	193,999	172,104	130,656
Depreciation and amortization	10,016	9,045	6,263
Operating income	100,323	85,767	68,666
Other income (expense):
Interest expense	(714)	(926)	(741)
Earnings of equity method investees	337	318	268
Other	735	781	507
Total other income (expense), net	358	173	34
Income before taxes	100,681	85,940	68,700
Income tax expense	(37,832)	(32,463)	(26,120)
Net income	$ 62,849	$ 53,477	$ 42,580
Earnings Per Share, Basic and Diluted [Abstract]
Basic	$ 4.96	$ 4.24	$ 3.42
Diluted	$ 4.95	$ 4.23	$ 3.40
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]
Weighted Average Number of Shares Outstanding, Basic	12,675	12,616	12,464
Weighted Average Number of Shares Outstanding, Diluted	12,709	12,647	12,513