Pensions and Postretirement Benefits Other than Pensions - Projected Benefit Obligation, Accumulated Benefit Obligation and Fair Value of Plan Assets for Pension Plans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Projected benefit obligation exceeds plan assets, Projected benefit obligation	$ 1,438,995	$ 1,267,763
Projected benefit obligation exceeds plan assets, Accumulated benefit obligation	1,435,193	1,264,377
Projected benefit obligation exceeds plan assets, Fair value of plan assets	1,005,574	907,131
Accumulated benefit obligation exceeds plan assets, Projected benefit obligation	1,438,995	1,267,763
Accumulated benefit obligation exceeds plan assets, Accumulated benefit obligation	1,435,193	1,264,377
Accumulated benefit obligation exceeds plan assets, Fair value of plan assets	$ 1,005,574	$ 907,131