Pension and Post-Retirement Benefit Plans - Schedule of Components of Net Periodic Pension Cost (Detail) - Pension Plans [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefit earned during the period	$ 444	$ 321
Interest cost on projected benefit obligation	1,769	1,862
Expected return on plan assets	(2,266)	(2,272)
Amortization of prior service cost	101	72
Amortization of actuarial loss	1,304	1,062
Total non-service cost	908	724
Net periodic pension cost	$ 1,352	$ 1,045