Components of net periodic pension cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service credit	$ (950)	$ (950)
Recognized net actuarial losses	5,025	2,126
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Interest Cost	7,403	7,461
Expected return on plan assets	(11,056)	(11,630)
Defined Benefit Plan Future Amortization Of Gain Loss	4,465	2,018
Total net periodic pension cost	812	(2,151)
Other Pension Plans Defined Benefit Member
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Interest Cost	407	415
Expected return on plan assets	(589)	(606)
Defined Benefit Plan Future Amortization Of Gain Loss	311	108
Total net periodic pension cost	$ 129	$ (83)