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, 2014	Dec. 31, 2013
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Projected benefit obligation exceeds plan assets, Projected benefit obligation	$ 1,562,333	$ 1,404,422
Projected benefit obligation exceeds plan assets, Accumulated benefit obligation	1,558,908	1,401,109
Projected benefit obligation exceeds plan assets, Fair value of plan assets	1,188,673	1,112,314
Accumulated benefit obligation exceeds plan assets, Projected benefit obligation	1,562,333	1,404,422
Accumulated benefit obligation exceeds plan assets, Accumulated benefit obligation	1,558,908	1,401,109
Accumulated benefit obligation exceeds plan assets, Fair value of plan assets	$ 1,188,673	$ 1,112,314