Employee Retirement and Postretirement Benefits - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plans
Components of net periodic benefit cost:
Service cost	$ 793	$ 908	$ 2,379	$ 2,724
Interest cost	3,043	3,434	9,129	10,302
Expected return on plan assets	(4,633)	(4,938)	(13,899)	(14,814)
Amortizations:
Prior service cost	214	214	642	642
Unrecognized net loss (gain)	2,206	2,136	6,618	6,408
Net periodic benefit cost	1,623	1,754	4,869	5,262
Postretirement Benefits
Components of net periodic benefit cost:
Service cost	160	205	480	615
Interest cost	271	364	813	1,092
Amortizations:
Prior service cost	23	23	69	69
Unrecognized net loss (gain)	(61)	16	(183)	48
Net periodic benefit cost	$ 393	$ 608	$ 1,179	$ 1,824