Benefits Expected to Be Paid from Pension and Other Postretirement Benefit Plans, Which Reflect Future Years of Services and Medicare Subsidy Expected to Be Received (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
2013	$ 28,818
2014	30,254
2015	31,673
2016	33,172
2017	34,763
2018 - 2022	194,789
Defined Benefit Plan, Expected Future Benefit Payments, Total	353,469
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
2013	3,942
2014	3,930
2015	3,669
2016	3,516
2017	3,547
2018 - 2022	16,023
Defined Benefit Plan, Expected Future Benefit Payments, Total	$ 34,627