Pension and Other Postretirement Benefits - Fair Values of Pension Plan Assets by Asset Category (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	$ 198,367	$ 173,154
Large-cap fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	75,306	62,151
Mid-cap fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	13,511	11,581
Small-cap fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	19,473	15,955
Government bond fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	25,520	24,385
Corporate bond fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	21,679	21,819
Fixed income fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	42,847	37,231
Cash & equivalents [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	31	32
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	31	32
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Large-cap fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mid-cap fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Small-cap fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Government bond fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate bond fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fixed income fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash & equivalents [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	31	32
Significant Observable Inputs (Level 2) [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	198,336	173,122
Significant Observable Inputs (Level 2) [Member] | Large-cap fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	75,306	62,151
Significant Observable Inputs (Level 2) [Member] | Mid-cap fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	13,511	11,581
Significant Observable Inputs (Level 2) [Member] | Small-cap fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	19,473	15,955
Significant Observable Inputs (Level 2) [Member] | Government bond fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	25,520	24,385
Significant Observable Inputs (Level 2) [Member] | Corporate bond fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	21,679	21,819
Significant Observable Inputs (Level 2) [Member] | Fixed income fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category	42,847	37,231
Significant Observable Inputs (Level 2) [Member] | Cash & equivalents [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Significant Unobservable Inputs (Level 3) [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Significant Unobservable Inputs (Level 3) [Member] | Large-cap fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Significant Unobservable Inputs (Level 3) [Member] | Mid-cap fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Significant Unobservable Inputs (Level 3) [Member] | Small-cap fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Significant Unobservable Inputs (Level 3) [Member] | Government bond fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Significant Unobservable Inputs (Level 3) [Member] | Corporate bond fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Significant Unobservable Inputs (Level 3) [Member] | Fixed income fund [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category
Significant Unobservable Inputs (Level 3) [Member] | Cash & equivalents [Member]
Pension And Other Employee Benefit Plans [Line Items]
Fair values of pension plan assets by asset category