Pensions and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Credit) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 9,425	$ 11,132	$ 9,511
Interest cost	19,340	17,934	19,018
Expected return on plan assets	(32,944)	(30,884)	(32,328)
Amortization of transition amounts	2	3	2
Amortization of prior service cost	84	102	101
Recognized net actuarial losses	8,639	13,323	6,235
Settlement loss	290	658	747
Termination benefits	0	0	387
Net periodic benefit cost	4,836	12,268	3,673
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	538	687	694
Interest cost	1,107	1,050	1,265
Expected return on plan assets	0	0	0
Amortization of transition amounts	0	0	0
Amortization of prior service cost	(335)	(424)	(454)
Recognized net actuarial losses	182	552	529
Settlement loss	0	0	0
Termination benefits	0	0	0
Net periodic benefit cost	$ 1,492	$ 1,865	$ 2,034