Employee Benefit Plans - Components of Net Periodic Benefit Cost (Credit) (Detail) - Pension Plans [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Components of Net Periodic Benefit Cost (Credit):
Service cost	$ 223	$ 335	$ 453	$ 675
Interest cost	3,977	4,086	8,039	8,067
Expected return on plan assets	(7,583)	(6,455)	(15,366)	(12,560)
Amortization of:
Prior service cost				30
Net actuarial loss (gain)	1,245	1,552	2,523	2,884
Net periodic benefit cost (credit)	$ (2,138)	$ (482)	$ (4,351)	$ (904)