Total Investments Plans Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 611,284	$ 644,931
Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	479,529	516,428
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	119,669	116,198
Cash and Accrued Items
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	12,086	12,305
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	102,329	122,032
Level 1 | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	58,556	82,390
Level 1 | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	31,687	27,337
Level 1 | Cash and Accrued Items
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	12,086	12,305
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	505,186	521,323
Level 2 | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	417,204	432,462
Level 2 | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	87,982	88,861
Level 2 | Cash and Accrued Items
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,769	1,576
Level 3 | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,769	1,576
Level 3 | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 3 | Cash and Accrued Items
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets