Pension and Postretirement Benefits - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2011
Pensions and Benefit Restoration Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contribution	$ 39,000	$ 124,600,000
Total contribution expected to be paid for pension and benefit restoration plans	126,700,000	126,700,000
Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contribution	1,600,000	3,600,000
Total contribution expected to be paid for pension and benefit restoration plans	$ 6,600,000	$ 6,600,000