Net Income Allocation and Per Unit Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Basic and Diluted Earnings Per Limited Partner:
Net income	$ 15,554		$ 19,288
Less General Partner's interest in net income	88		109
Net income available to limited partners	15,466		19,179
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260- 10-45-60	1,930		2,665
Limited Partner's interest in net income under FASB ASC 260-10-45-60	$ 13,536		$ 16,514
Per unit data:
Basic and diluted net income available to limited partners	0.27		0.33
Less dilutive impact of theoretical distribution of earnings under FASB ASC 260- 10-45-60	0.03		0.04
Limited Partner's interest in net income under FASB ASC 260- 10-45-60	$ 0.24	[1]	$ 0.29	[1]
Weighted average number of Limited Partner units outstanding	57,294		57,511

[1] See Note 12 Earnings Per Limited Partner Unit.