Employee and Retiree Benefit Plans - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
	Mar. 31, 2010	Sep. 30, 2012
Pension and Other Postretirement Benefits Disclosure [Line Items]
Contributions to benefit plans		$ 37,900,000
Anticipated remaining funding to defined benefit pension and postretirement plans		7,500,000
Provisions of the March 2010 Health Care Reform	In March 2010, the United States Congress enacted a health care reform law. Along with other provisions, the law (a) eliminates the tax free status of federal subsidies to companies with qualified retiree prescription drug plans that are actuarially equivalent to Medicare Part D plans beginning in 2013; (b) imposes a 40% excise tax on high-cost health plans as defined in the law beginning in 2018; (c) eliminates lifetime or annual coverage limits and required coverage for preventative health services beginning in September 2010; and (d) imposed a fee of $2 (subsequently adjusted for inflation) for each person covered by a health insurance policy beginning in September 2010. In June 2012, the U.S. Supreme Court upheld the constitutionality of the health care reform law.
Excise tax rate imposed on high-cost health plans beginning 2018	40.00%
Government imposed fee for each person covered by health insurance policy	$ 2