Components of net periodic postretirement benefit cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pension and Other Postretirement Benefits Disclosure [Line Items]
Amortization of prior service credit	$ (950)	$ 0
Other Postretirement Benefit Plans Defined Benefit [Member]
Pension and Other Postretirement Benefits Disclosure [Line Items]
Defined Benefit Plan Service Cost	364	564
Defined Benefit Plan Interest Cost	1,712	1,712
Amortization of prior service credit	(950)	0
Defined Benefit Plan Amortization Of Net Gains Losses	0	473
Total net periodic pension cost	$ 1,126	$ 2,749