Employee Retirement and Postretirement Benefits - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Plans
Components of net periodic benefit cost:
Service cost	$ 752	$ 793
Interest cost	2,927	3,043
Expected return on plan assets	(4,758)	(4,633)
Amortizations:
Prior service cost	176	214
Unrecognized net (gain) loss	2,581	2,206
Net periodic benefit cost	1,678	1,623
Postretirement Benefits
Components of net periodic benefit cost:
Service cost	146	160
Interest cost	240	271
Amortizations:
Prior service cost	23	23
Unrecognized net (gain) loss	(114)	(61)
Net periodic benefit cost	$ 295	$ 393