Benefit Plans - Components of Net Periodic Pension Income for Qualified and Non-Qualified Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Interest cost	$ 5,542	$ 5,713	$ 6,681
Expected return on plan assets	(15,912)	(15,163)	(14,539)
Amortization of net loss	625	381	294
Total net periodic pension income	$ (9,745)	$ (9,069)	$ (7,564)