Earnings Per Limited Partner Unit - 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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic and Diluted Earnings Per Limited Partner:
Net income (loss)		$ (46)	$ (23,098)	$ 86,117	$ 51,542
Less General Partner’s interest in net income (loss)		(1)	(150)	600	319
Net income (loss) available to limited partners		(45)	(22,948)	85,517	51,223
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60				13,616	6,740
Limited Partner’s interest in net income (loss) under FASB ASC 260-10-45-60		$ (45)	$ (22,948)	$ 71,901	$ 44,483
Per unit data:
Basic and diluted net income (loss) available to limited partners			$ (0.46)	$ 1.85	$ 1.00
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60				0.30	0.14
Limited Partner’s interest in net income (loss) under FASB ASC 260-10-45-60	[1]		$ (0.46)	$ 1.55	$ 0.86
Weighted average number of Limited Partner units outstanding		45,246	49,943	46,253	51,431

[1] See Note 16 - Earnings Per Limited Partner Unit.