Benefit Plans - Components of Net Periodic Pension Income for Qualified and Non-Qualified Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Interest cost	$ 6,113	$ 5,542	$ 5,713
Expected return on plan assets	(16,453)	(15,912)	(15,163)
Amortization of net loss	264	625	381
Total net periodic pension income	$ (10,076)	$ (9,745)	$ (9,069)