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	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Projected benefit obligation exceeds plan assets, Projected benefit obligation	$ 1,463,026	$ 1,451,351
Projected benefit obligation exceeds plan assets, Accumulated benefit obligation	1,463,026	1,451,351
Accumulated benefit obligation exceeds plan assets, Projected benefit obligation	1,459,809	1,448,277
Accumulated benefit obligation exceeds plan assets, Accumulated benefit obligation	1,459,809	1,448,277
Projected benefit obligation exceeds plan assets, Fair value of plan assets	1,176,874	1,146,430
Accumulated benefit obligation exceeds plan assets, Fair value of plan assets	$ 1,176,874	$ 1,146,430