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 pension plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 624	$ 2,120	$ 4,988	$ 7,432
Interest cost	7,036	6,747	19,568	20,666
Expected return on plan assets	(7,356)	(7,826)	(22,629)	(23,849)
Amortization of prior service cost (credit)	6	(264)	(522)	(792)
Recognized actuarial loss (gain)	3,138	3,600	12,919	10,776
Curtailment gain			(8,639)
Settlement loss	5,233		5,233
Net periodic benefit cost	8,681	4,377	10,918	14,233
Postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Service (credit) cost	(1)	11	41	51
Interest cost	270	129	896	1,033
Recognized actuarial loss (gain)	34	(138)	111	12
Net periodic benefit cost	$ 303	$ 2	$ 1,048	$ 1,096