Pension and other postretirement benefits - amounts recognized in consolidated balance sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Payroll and benefit-related liabilities	$ (115,981)	$ (104,670)
Pension and postretirement benefit liabilities	(82,719)	(92,914)
Pension
Defined Benefit Plan Disclosure [Line Items]
Other assets	2,449	2,837
Payroll and benefit-related liabilities	(1,617)	(1,729)
Pension and postretirement benefit liabilities	(47,768)	(54,771)
Accumulated other comprehensive loss	213,989	205,910
Amounts recognized in balance sheet	167,053	152,247
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Other assets	0	0
Payroll and benefit-related liabilities	(5,091)	(3,972)
Pension and postretirement benefit liabilities	(34,951)	(38,143)
Accumulated other comprehensive loss	1,916	364
Amounts recognized in balance sheet	$ (38,126)	$ (41,751)