Employee Benefit Plans - Components of Net Periodic Benefit Cost (Credit) (Detail) - Pension Plans [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Components of Net Periodic Benefit Cost (Credit):
Service cost	$ 217	$ 373	$ 670	$ 1,048
Interest cost	3,822	4,191	11,861	12,258
Expected return on plan assets	(7,315)	(6,295)	(22,681)	(18,855)
Amortization of:
Prior service cost				30
Net actuarial loss (gain)	1,213	1,285	3,736	4,169
Net periodic benefit cost (credit)	$ (2,063)	$ (446)	$ (6,414)	$ (1,350)