Estimated Future Benefit Payments for Defined Benefit Pension and Postretirement Benefit Plans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Benefit of Medicare Part D Subsidy
Schedule of Pension and Other Postretirement Benefits Expected Benefit Payments [Line Items]
Benefit of Medicare Part D Subsidy - 2013	$ (300)
Benefit of Medicare Part D Subsidy - 2014	(300)
Benefit of Medicare Part D Subsidy - 2015	(300)
Benefit of Medicare Part D Subsidy - 2016	(300)
Benefit of Medicare Part D Subsidy - 2017	(300)
Benefit of Medicare Part D Subsidy - 2018 - 2022	(1,300)
Defined benefit pension plans
Schedule of Pension and Other Postretirement Benefits Expected Benefit Payments [Line Items]
Benefit payments - 2013	34,006
Benefit payments - 2014	26,370
Benefit payments - 2015	27,352
Benefit payments - 2016	29,015
Benefit payments - 2017	30,352
Benefit payments - 2018 - 2022	173,602
Postretirement Benefit Plans Before Subsidy
Schedule of Pension and Other Postretirement Benefits Expected Benefit Payments [Line Items]
Benefit payments - 2013	3,000
Benefit payments - 2014	2,900
Benefit payments - 2015	2,800
Benefit payments - 2016	2,800
Benefit payments - 2017	2,800
Benefit payments - 2018 - 2022	$ 12,400