Components of Net Periodic Benefit Cost (Net Periodic Benefit Cost (Increase)) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	307	312	614	624
Expected return on plan assets	(638)	(612)	(1,276)	(1,224)
Amortization of prior service cost	0	0	0	0
Amortization of the net loss	230	236	460	472
Net periodic (increase) benefit cost	(101)	(64)	(202)	(128)
Other post-retirement benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	26	37	52	75
Interest cost	218	285	436	569
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	0	0	0
Amortization of the net loss	(169)	0	(338)	0
Net periodic (increase) benefit cost	$ 75	$ 322	$ 150	$ 644