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, 2019	Dec. 31, 2018
All Plans, Less Spectrum
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation exceeds plan assets, Projected benefit obligation	$ 1,052,824	$ 1,409,380
Accumulated benefit obligation exceeds plan assets, Projected benefit obligation	1,051,298	1,406,263
Projected benefit obligation exceeds plan assets, Fair value of plan assets	909,890	1,261,130
Spectrum Plan
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation exceeds plan assets, Projected benefit obligation	500,739	0
Accumulated benefit obligation exceeds plan assets, Projected benefit obligation	500,739	0
Projected benefit obligation exceeds plan assets, Fair value of plan assets	$ 516,666	$ 0