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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic and Diluted Earnings Per Limited Partner:
Net income (loss)	$ (8,005)	$ (13,332)	$ 76,955	$ 44,647
Less General Partner’s interest in net income (loss)	(49)	(79)	445	259
Limited Partners’ interest in net income (loss)	(7,956)	(13,253)	76,510	44,388
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60			11,610	5,420
Limited Partner’s interest in net income (loss) under FASB ASC 260-10-45-60	$ (7,956)	$ (13,253)	$ 64,900	$ 38,968
Per unit data:
Basic and diluted net income (loss) available to limited partners	$ (0.15)	$ (0.24)	$ 1.39	$ 0.79
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60			0.21	0.09
Limited Partner’s interest in net income (loss) under FASB ASC 260-10-45-60	$ (0.15)	$ (0.24)	$ 1.18	$ 0.70
Weighted average number of Limited Partner units outstanding	53,938	55,888	55,157	55,888