Assets Measured at Fair Value on Recurring Basis for Pension Plan (Detail) (Pension Plans, USD $)
In Thousands, unless otherwise specified

Dec. 31, 2012

Dec. 31, 2011

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

$ 72,411

$ 59,700

Equity Funds

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

34,742

29,094

Fixed Income Securities

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

34,251

27,697

Equity And Debt Securities

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

3,418

2,909

Fair Value, Inputs, Level 1

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

72,411

59,700

Fair Value, Inputs, Level 1 | Equity Funds

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

34,742

29,094

Fair Value, Inputs, Level 1 | Fixed Income Securities

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

34,251

27,697

Fair Value, Inputs, Level 1 | Equity And Debt Securities

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

3,418

2,909

Fair Value, Inputs, Level 2

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

Fair Value, Inputs, Level 2 | Equity Funds

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

Fair Value, Inputs, Level 2 | Fixed Income Securities

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

Fair Value, Inputs, Level 2 | Equity And Debt Securities

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

Fair Value, Inputs, Level 3

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

Fair Value, Inputs, Level 3 | Equity Funds

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

Fair Value, Inputs, Level 3 | Fixed Income Securities

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis

Fair Value, Inputs, Level 3 | Equity And Debt Securities

Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]

Assets measured at fair value on recurring basis