Plan Assets Measured and Reported in Financial Statements 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	$ 456,445	$ 406,163
Collective trust funds | US equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	174,735	148,435
Collective trust funds | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	164,998	147,756
Collective trust funds | International fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	41,523	36,580
US government and US government agency securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	31,434	35,944
US corporate debt instruments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21,171	20,514
International corporate debt instruments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,996	5,455
Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8,741	5,083
Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8,847	6,396
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,520	1,422
Level 1 | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,520	1,422
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	454,925	404,741
Level 2 | Collective trust funds | US equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	174,735	148,435
Level 2 | Collective trust funds | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	164,998	147,756
Level 2 | Collective trust funds | International fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	41,523	36,580
Level 2 | US government and US government agency securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	31,434	35,944
Level 2 | US corporate debt instruments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21,171	20,514
Level 2 | International corporate debt instruments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,996	5,455
Level 2 | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,221	3,661
Level 2 | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 8,847	$ 6,396