Net Income Allocation and Per Unit Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Basic and Diluted Earnings Per Limited Partner:
Net income		$ 30,182	$ 18,275
Less General Partner’s interest in net income		175	105
Limited Partners’ interest in net income		30,007	18,170
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60		4,740	2,446
Limited Partner’s interest in net income under FASB ASC 260-10-45-60		$ 25,267	$ 15,724
Per unit data:
Basic and diluted net income available to limited partners		$ 0.53	$ 0.33
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260-10-45-60		0.08	0.05
Limited Partner’s interest in net income under FASB ASC 260-10-45-60	[1]	$ 0.45	$ 0.28
Basic and Diluted		55,887	55,887

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