Postretirement Benefits - Components of Net Periodic Pension Costs and Post-Retirement Benefit Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Net amortization	$ 8,474	$ 15,095	$ 12,436
Net periodic benefit cost	24,134	32,593	28,828
Funded defined benefit pension
Retirement Benefits [Abstract]
Service cost—benefits earned during the period	19,929	21,092	17,942
Interest cost on projected benefit obligation	23,827	22,303	22,124
Expected return on assets	(27,862)	(25,547)	(23,597)
Net amortization	8,211	15,003	12,281
Recognition of actuarial loss	29	(258)	78
Net periodic benefit cost	$ 24,134	$ 32,593	$ 28,828