Pension and Postretirement Benefits Other Than Pension Plans - Net Periodic Pension (Income) Expense (Detail) - Pension Plan [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]
Interest cost	$ 803	$ 901	$ 1,614	$ 1,815
Expected return on plan assets	(1,070)	(1,011)	(2,172)	(2,047)
Amortization of net actuarial loss	264	297	519	579
Total net periodic pension (income) expense	$ (3)	$ 187	$ (39)	$ 347