Employee Retirement and Postretirement Benefits - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Defined Benefit Plans
Components of net periodic benefit cost:
Service cost	$ 908	$ 770	$ 2,724	$ 2,310
Interest cost	3,434	3,495	10,302	10,485
Expected return on plan assets	(4,938)	(4,690)	(14,814)	(14,070)
Amortizations:
Prior service cost	214	197	642	591
Unrecognized net loss	2,136	1,276	6,408	3,828
Net periodic benefit cost	1,754	1,048	5,262	3,144
Postretirement Benefits
Components of net periodic benefit cost:
Service cost	205	206	615	618
Interest cost	364	416	1,092	1,248
Amortizations:
Prior service cost	23	16	69	48
Unrecognized net loss	16	19	48	57
Net periodic benefit cost	$ 608	$ 657	$ 1,824	$ 1,971