Components of Net Periodic Benefit Cost (Net Periodic Benefit Cost (Increase)) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	$ 0	$ 0
Interest cost	307	312
Expected return on plan assets	(638)	(612)
Amortization of prior service cost	0	0
Amortization of the net loss (gain)	230	236
Net periodic benefit (increase) cost	(101)	(64)
Other post-retirement benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	26	38
Interest cost	218	284
Expected return on plan assets	0	0
Amortization of prior service cost	0	0
Amortization of the net loss (gain)	(169)	0
Net periodic benefit (increase) cost	$ 75	$ 322