Common Unit Repurchase Plans and Retirement - Additional Information (Detail) - USD ($) shares in Thousands		1 Months Ended				3 Months Ended				12 Months Ended	60 Months Ended	67 Months Ended
	Jul. 02, 2018	Sep. 30, 2018	Aug. 31, 2018		Jul. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018		Sep. 30, 2018	Sep. 30, 2017	Jan. 31, 2018	Feb. 28, 2018	Dec. 31, 2017	Jul. 30, 2015
Capital Unit [Line Items]
Company's common units authorized for repurchase			5,550		3,000							2,200	5,500
Fourth Amendment
Capital Unit [Line Items]
Availability required to repurchase common units	$ 45,000,000
Percentage of the maximum facility size on a historical proforma and forward-looking basis	15.00%
Non Seasonal maximum borrowing capacity under revolving credit facility	$ 300,000,000														$ 300,000,000
Minimum fixed charge coverage ratio for distributions to unit holders or to repurchase common units	115.00%
Repurchase Plan
Capital Unit [Line Items]
Company's common units repurchased and retired		191	114		125	430	1,089	1,281		2,800	5,137	2,700
Company's common units authorized for repurchase			5,550		2,900							2,200	5,500
Total Common Units remain available for repurchase		5,359	5,550	[1]	3,005	5,359	3,130	4,219	[2]	5,359	2,207			2,207
Common Stock Available for Repurchase Under Open Market Transactions
Capital Unit [Line Items]
Company's common units authorized for repurchase			3,050
Common Stock Available for Repurchase Under Privately Negotiated Transactions
Capital Unit [Line Items]
Company's common units authorized for repurchase			2,500

[1] In August 2018, the Board authorized an increase in the number of Common Units available for repurchase from 2.9 million to 5.55 million.

[2] In February 2018, the Board authorized an increase in the number of Common Units available for repurchase from 2.2 million to 5.5 million.