Financial Assets Accounted for at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 563,303	[1]	$ 531,105	[1]	$ 507,064
Pension Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	218,145	[2]	229,842	[2]
Pension Benefits | International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	107,647	[3]	90,056	[3]
Pension Benefits | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	142,967	[4]	129,608	[4]
Pension Benefits | Absolute Return
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	80,714	[5]	78,432	[5]
Pension Benefits | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13,830		3,167
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,611	[1]	7,681	[1]	7,985
Postretirement Benefits | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,611	[4]	7,681	[4]
Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	247,463	[1]	228,592	[1]
Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	153,465	[2]	173,710	[2]
Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Benefits | International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18,977	[3]
Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Benefits | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	51,306	[4]	46,308	[4]
Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Benefits | Absolute Return
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9,885	[5]	5,407	[5]
Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Benefits | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13,830		3,167
Quoted Prices in Active Markets for Similar Items (Level 2) | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	245,011	[1]	229,488	[1]
Quoted Prices in Active Markets for Similar Items (Level 2) | Pension Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64,680	[2]	56,132	[2]
Quoted Prices in Active Markets for Similar Items (Level 2) | Pension Benefits | International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	88,670	[3]	90,056	[3]
Quoted Prices in Active Markets for Similar Items (Level 2) | Pension Benefits | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	91,661	[4]	83,300	[4]
Quoted Prices in Active Markets for Similar Items (Level 2) | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,611	[1]	7,681	[1]
Quoted Prices in Active Markets for Similar Items (Level 2) | Postretirement Benefits | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,611	[4]	7,681	[4]
Unobservable inputs (Level 3) | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	70,829	[1]	73,025	[1]	69,399
Unobservable inputs (Level 3) | Pension Benefits | Absolute Return
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 70,829	[5]	$ 73,025	[5]

[1] See Note 17 "Pension Plans and Other Postretirement Benefits" for further discussion on fair value measurements of our pension and postretirement assets.

[2] Consists primarily of U.S. equity securities covering a diverse group of companies and U.S. stock funds that primarily track or are actively managed and measured against indices including the S&P 500 and the Russell 2000.

[3] Consists primarily of international equity funds which include stocks and debt obligations of non-U.S. entities that primarily track or are actively managed and measured against various MSCI indices.

[4] Consists primarily of fixed income mutual funds, corporate bonds, U.S. Treasury notes, other government securities and insurance policies.

[5] Consists primarily of holdings in private investment companies. See additional information about the Absolute Return investments below.