Pension and Post-Retirement Benefit Plans - Schedule of Components of Net Periodic Pension Cost (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
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefit earned during the period	$ 444	$ 321	$ 888	$ 642
Interest cost on projected benefit obligation	1,769	1,862	3,538	3,724
Expected return on plan assets	(2,266)	(2,272)	(4,532)	(4,544)
Amortization of prior service cost	101	72	202	144
Amortization of actuarial loss	1,304	1,062	2,608	2,124
Total non-service cost	908	723	1,816	1,447
Net periodic pension cost	$ 1,352	$ 1,045	$ 2,704	$ 2,090