Benefit Payments, Reflected Expected Future Service as Appropriate which are Expected to be Paid in Future Years from Assets of Plans or by Company (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
2013	$ 31,968
2014	32,978
2015	33,770
2016	34,461
2017	35,627
2018-2022	202,836
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
2013	7,231
2014	7,512
2015	7,778
2016	8,074
2017	8,379
2018-2022	$ 47,829

Benefit Payments, Reflected Expected Future Service as Appropriate which are Expected to be Paid in Future Years from Assets of Plans or by Company (Detail) (USD $)
In Thousands, unless otherwise specified

Dec. 31, 2012

Pension Benefits

Defined Benefit Plan Disclosure [Line Items]

$ 31,968

32,978

33,770

34,461

35,627

202,836