Net Income Allocation and Per Unit Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic and Diluted Earnings Per Limited Partner:
Net income (loss)		$ (13,332)	$ (3,238)	$ 44,647	$ 64,029
Less General Partner's interest in net income		(79)	(19)	259	362
Net income (loss) available to limited partners		(13,253)	(3,219)	44,388	63,667
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60				5,420	9,313
Limited Partner's interest in net income (loss) under FASB ASC 260-10-45-60		$ (13,253)	$ (3,219)	$ 38,968	$ 54,354
Per unit data:
Basic and diluted net income (loss) available to limited partners		$ (0.24)	$ (0.06)	$ 0.79	$ 1.11
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60				0.09	0.16
Limited Partner's interest in net income (loss) under FASB ASC 260-10-45-60	[1]	$ (0.24)	$ (0.06)	$ 0.70	$ 0.95
Weighted average number of Limited Partner units outstanding		55,888	57,188	55,888	57,237

[1] See Note 13 Earnings Per Limited Partner Unit.