Changes in Fair Value of Plan Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	$ 243,379		$ 215,775
Cash and Cash Equivalents
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	4,670	[1]	6,403	[1]
US Large Cap
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	32,165		29,329
U.S. Mid-Cap And Small-Cap
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	3,638		3,346
Equity Securities International
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	108,403	[2]	80,409	[2]
Equity Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	144,206		113,084
Corporate Bonds - Domestic
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	16,536		18,371
Corporate Bonds - International
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	20,575		28,950
UK Index-Linked Gilts
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	22,492		22,041
Diversified Domestic Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	5,502		1,594
Total Fixed Income Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	65,105		70,956
U.S. Real Estate
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	1,445	[3]	1,289	[3]
International Real Estate
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	15,766	[3]	12,463	[3]
Other Investment
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	12,187	[4]	11,580	[4]
Quoted Prices In Active Markets For Identical Assets (Level 1)
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	15,655
Quoted Prices In Active Markets For Identical Assets (Level 1) | Cash and Cash Equivalents
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	448	[1]
Quoted Prices In Active Markets For Identical Assets (Level 1) | Equity Securities International
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	15,207	[2]
Quoted Prices In Active Markets For Identical Assets (Level 1) | Equity Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	15,207
Significant Observable Inputs (Level 2)
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	215,537		204,195
Significant Observable Inputs (Level 2) | Cash and Cash Equivalents
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	4,222	[1]	6,403	[1]
Significant Observable Inputs (Level 2) | US Large Cap
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	32,165		29,329
Significant Observable Inputs (Level 2) | U.S. Mid-Cap And Small-Cap
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	3,638		3,346
Significant Observable Inputs (Level 2) | Equity Securities International
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	93,196	[2]	80,409	[2]
Significant Observable Inputs (Level 2) | Equity Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	128,999		113,084
Significant Observable Inputs (Level 2) | Corporate Bonds - Domestic
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	16,536		18,371
Significant Observable Inputs (Level 2) | Corporate Bonds - International
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	20,575		28,950
Significant Observable Inputs (Level 2) | UK Index-Linked Gilts
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	22,492		22,041
Significant Observable Inputs (Level 2) | Diversified Domestic Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	5,502		1,594
Significant Observable Inputs (Level 2) | Total Fixed Income Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	65,105		70,956
Significant Observable Inputs (Level 2) | U.S. Real Estate
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	1,445	[3]	1,289	[3]
Significant Observable Inputs (Level 2) | International Real Estate
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	15,766	[3]	12,463	[3]
Significant Unobservable Inputs (Level 3)
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	12,187		11,580
Significant Unobservable Inputs (Level 3) | Other Investment
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Defined benefit plan, fair value of plan assets	$ 12,187	[4]	$ 11,580	[4]

[1] Cash and cash equivalents consist of traditional domestic and foreign highly liquid short-term securities with the goal of providing liquidity and preservation of capital while maximizing return on assets.

[2] The International category consists of investment funds focused on companies operating in developed and emerging markets outside of the U.S. These investments target broad diversification across large and mid/small-cap companies and economic sectors.

[3] U.S. and International real estate consists primarily of equity and debt investments made, directly or indirectly, in various interests in unimproved and improved real properties.

[4] Other investments consist of insurance and reinsurance contracts securing the retirement benefits. The fair value of these contracts was calculated at the discount value of premiums paid by the Company, less expenses charged by the insurance providers. The insurance providers with which the Company has placed these contracts are well-known financial institutions with an established history of providing insurance services.