Earnings Per Limited Partner Units (Details 1) (USD $) In Thousands, except Share data, 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
Basic and Diluted Earnings Per Limited Partner:
Net income	$ (5,635)	$ (11,789)	$ 40,482	$ 2,931	$ (26,698)	$ (18,197)	$ 48,681	$ 20,558	$ 25,989		$ 24,344		$ 28,320
Less General Partners' interest in net income									136		115		128
Net income available to limited partners	(5,605)	(11,727)	40,269	2,916	(26,566)	(18,109)	48,445	20,459	25,853		24,229		28,192
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60 *									1,142		574		1,258
Limited partner's interest in net income under FASB ASC 260-10-45-60									$ 24,711		$ 23,655		$ 26,934
Per unit data:
Basic and diluted net income available to limited partners									0.42		0.36		0.40
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60*									0.02		0.01		0.02
Limited Partner's interest in net income under FASB ASC 260-10-45-60	(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]
Weighted average number of limited partnership units outstanding									61,931		66,822		70,019

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