Net Income Allocation and Per Unit Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2011
Basic and Diluted Earnings Per Limited Partner:
Net income	$ (13,937)	$ (7,588)	$ 41,679	$ 9,752	$ (5,635)	$ (11,789)	$ 40,482	$ 2,931	$ 29,906		$ 25,989		$ 24,344
Less General Partners' interest in net income									159		136		115
Net income available to limited partners	(13,859)	(7,547)	41,454	9,699	(5,605)	(11,727)	40,269	2,916	29,747		25,853		24,229
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60									2,010	[1]	1,142	[1]	574	[1]
Limited Partner's interest in net income under FASB ASC 260-10-45-60									$ 27,737		$ 24,711		$ 23,655
Per unit data:
Basic and diluted net income available to limited partners									0.50		0.42		0.36
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60									0.03	[1]	0.02	[1]	0.01	[1]
Limited Partner's interest in net income under FASB ASC 260-10-45-60	$ (0.24)	$ (0.13)	$ 0.58	$ 0.15	$ (0.09)	$ (0.19)	$ 0.55	$ 0.05	$ 0.47	[2]	$ 0.40	[2]	$ 0.35	[2]
Weighted average number of Limited Partner units outstanding									59,409		61,931		66,822

[1] In any accounting period where the Partnership's aggregate net income exceeds its aggregate distribution for such period, the Partnership is required as per FASB ASC 260-10-45-60 to present net income per limited partner unit as if all of the earnings for the period were distributed, based on the contractual participation rights of the security to share in earnings, regardless of whether those earnings would actually be distributed during a particular period from an economic or practical perspective. This allocation does not impact the Partnership's overall net income or other financial results.

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