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, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
Basic and Diluted Earnings Per Limited Partner:
Net income	$ (25,828)		$ (9,592)		$ 52,216		$ 19,288		$ (13,937)		$ (7,588)		$ 41,679		$ 9,752		$ 36,084		$ 29,906		$ 25,989
Less General Partners' interest in net income																	203		159		136
Net income available to limited partners	(25,682)		(9,538)		51,922		19,179		(13,859)		(7,547)		41,454		9,699		35,881		29,747		25,853
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60																	3,195	[1]	2,010	[1]	1,142	[1]
Limited Partner's interest in net income under FASB ASC 260-10-45-60																	$ 32,686		$ 27,737		$ 24,711
Per unit data:
Basic and diluted net income available to limited partners																	0.62		0.50		0.42
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60																	0.05	[1]	0.03	[1]	0.02	[1]
Limited Partner's interest in net income under FASB ASC 260-10-45-60	$ (0.45)	[2]	$ (0.17)	[2]	$ 0.75	[2]	$ 0.29	[2]	$ (0.24)	[2]	$ (0.13)	[2]	$ 0.58	[2]	$ 0.15	[2]	$ 0.57	[2],[3]	$ 0.47	[2],[3]	$ 0.40	[3]
Weighted average number of Limited Partner units outstanding																	57,476		59,409		61,931

[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 terms of the Partnership agreement, 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] The sum of the quarters do not add-up to the total due to the weighting of Limited Partner Units outstanding, rounding or the theoretical effects of FASB ASC 260-10-45-60 to Master Limited Partners earnings per unit.

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