Fair Values and Percentage of Partnership's Pension Plan Assets by Asset Category (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets	$ 60,028
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	60,028
Significant Other Observable Inputs Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets
Significant Unobservable Inputs Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets
Corporate and U.S. government bond fund
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets	47,364	[1]
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	47,364	[1]
Corporate and U.S. government bond fund | Significant Other Observable Inputs Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets		[1]
Corporate and U.S. government bond fund | Significant Unobservable Inputs Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets		[1]
U.S. large-cap equity
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets	9,123	[1]
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	9,123	[1]
U.S. large-cap equity | Significant Other Observable Inputs Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets		[1]
U.S. large-cap equity | Significant Unobservable Inputs Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets		[1]
International equity
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets	3,082	[1]
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	3,082	[1]
International equity | Significant Other Observable Inputs Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets		[1]
International equity | Significant Unobservable Inputs Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets		[1]
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets	459
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	459
Cash | Significant Other Observable Inputs Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets
Cash | Significant Unobservable Inputs Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair values of the Partnership's pension plan assets

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