Fair Values and Percentage of Partnership's Pension Plan Assets by Asset Category (Detail) (USD $)	Sep. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Percentage of the Partnership's pension plan assets	100.00%
Quoted Prices in Active Markets for Identical Assets Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets	$ 65,379,000
Corporate and U.S. government bond fund
Defined Benefit Plan Disclosure [Line Items]
Percentage of the Partnership's pension plan assets	79.00%	[1]
Corporate and U.S. government bond fund | Quoted Prices in Active Markets for Identical Assets Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets	52,204,000	[1]
U.S. large-cap equity
Defined Benefit Plan Disclosure [Line Items]
Percentage of the Partnership's pension plan assets	15.00%	[1]
U.S. large-cap equity | Quoted Prices in Active Markets for Identical Assets Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets	9,774,000	[1]
International equity
Defined Benefit Plan Disclosure [Line Items]
Percentage of the Partnership's pension plan assets	5.00%	[1]
International equity | Quoted Prices in Active Markets for Identical Assets Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets	3,093,000	[1]
Cash
Defined Benefit Plan Disclosure [Line Items]
Percentage of the Partnership's pension plan assets	1.00%
Cash | Quoted Prices in Active Markets for Identical Assets Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets	$ 308,000

[1] Represent investments in Vanguard funds that seek to replicate the asset category description.