Fair values of Company's pension plan assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	$ 30,590	$ 29,341	$ 26,839
Cash and certificates of deposit
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	3,253	7,815
Equity Securities Industrials
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	2,676	1,064
Equity Securities Financials
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	2,353	1,669
Equity Securities Telecommunication services
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	1,121	765
Equity Securities Consumer
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	3,515	3,429
Equity Securities Health care
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	1,900	1,594
Equity Securities Information technology
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	2,328	1,416
Equity Securities Energy
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	2,645	811
Equity Securities Other
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	156	775
Total equity securities
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	17,901	11,523
Fixed income securities U. S. Government Agencies
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	619
Fixed income securities Corporate bonds
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	9,283	9,251
Fixed income securities Other
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	153	133
Equity Securities Materials
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	1,207
Quoted Prices in Active Markets for Identical Assets (Level 1)
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	21,307	19,471
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and certificates of deposit
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	3,253	7,815
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Securities Industrials
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	2,676	1,064
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Securities Financials
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	2,353	1,669
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Securities Telecommunication services
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	1,121	765
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Securities Consumer
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	3,515	3,429
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Securities Health care
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	1,900	1,594
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Securities Information technology
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	2,328	1,416
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Securities Energy
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	2,645	811
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Securities Other
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	156	775
Quoted Prices in Active Markets for Identical Assets (Level 1) | Total equity securities
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	17,901	11,523
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed income securities U. S. Government Agencies
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed income securities Corporate bonds
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed income securities Other
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	153	133
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Securities Materials
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	1,207
Significant Other Observable Inputs (Level 2)
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	9,283	9,870
Significant Other Observable Inputs (Level 2) | Cash and certificates of deposit
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Other Observable Inputs (Level 2) | Fixed income securities U. S. Government Agencies
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	619
Significant Other Observable Inputs (Level 2) | Fixed income securities Corporate bonds
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	9,283	9,251
Significant Unobservable Inputs (Level 3) | Cash and certificates of deposit
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Unobservable Inputs (Level 3) | Equity Securities Industrials
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Unobservable Inputs (Level 3) | Equity Securities Financials
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Unobservable Inputs (Level 3) | Equity Securities Telecommunication services
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Unobservable Inputs (Level 3) | Equity Securities Consumer
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Unobservable Inputs (Level 3) | Equity Securities Health care
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Unobservable Inputs (Level 3) | Equity Securities Information technology
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Unobservable Inputs (Level 3) | Equity Securities Energy
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Unobservable Inputs (Level 3) | Equity Securities Other
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Unobservable Inputs (Level 3) | Total equity securities
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Unobservable Inputs (Level 3) | Fixed income securities U. S. Government Agencies
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Unobservable Inputs (Level 3) | Fixed income securities Corporate bonds
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	0	0
Significant Unobservable Inputs (Level 3) | Fixed income securities Other
Schedule Of Defined Benefit Plan Funded Status Of Plan [Line Items]
Asset Category:	$ 0	$ 0