Selected Quarterly Financial Data (unaudited) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2010
Nature of the Partnership's business
Sales	$ 174,046	$ 232,476	$ 629,592	$ 461,474	$ 153,172	$ 246,772	$ 731,865	$ 459,501	$ 1,497,588		$ 1,591,310		$ 1,212,776
Gross profit for product, installation and service	32,783	46,550	125,994	92,450	30,493	51,633	166,636	105,207	297,777		353,969
Operating income (loss)	(7,543)	(20,051)	72,879	8,581	(41,297)	(28,266)	87,959	43,651	53,866		62,047		58,584
Income (loss) before income taxes	(10,457)	(22,434)	69,873	5,583	(43,867)	(30,784)	84,149	37,569	42,565		47,067		43,952
Net income (loss)	(5,635)	(11,789)	40,482	2,931	(26,698)	(18,197)	48,681	20,558	25,989		24,344		28,320
Limited Partners' interest in net income	$ (5,605)	$ (11,727)	$ 40,269	$ 2,916	$ (26,566)	$ (18,109)	$ 48,445	$ 20,459	$ 25,853		$ 24,229		$ 28,192
Net income (loss) per Limited Partner unit:
Basic and diluted income per Limited Partner Unit (1):	(0.09)	(0.19)	0.55	0.05	(0.40)	(0.27)	0.61	0.26	0.40	[1]	0.35	[1]	0.38	[1]

[1] See Note 17 Earnings Per Limited Partner Units.