Employee Benefit Plans - Components of Net Periodic Benefit Cost (Credit) (Detail) - Pension Plans [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Components of Net Periodic Benefit Cost (Credit):
Service cost	$ 230	$ 340
Interest cost	4,062	3,981
Expected return on plan assets	(7,783)	(6,105)
Amortization of:
Prior service cost		30
Net actuarial loss (gain)	1,278	1,332
Net periodic benefit cost (credit)	$ (2,213)	$ (422)