Pension Benefit and Other Postretirement Benefit Plans - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2011	Sep. 30, 2012 President and Chief Executive Officer	Mar. 31, 2012 Retirement Health and Life Insurance Benefits	Jun. 30, 2012 Retirement Health and Life Insurance Benefits
Pension and Other Postretirement Benefits Disclosure [Line Items]
Special termination benefit				$ 2,100,000	$ 1,600,000	$ 2,300,000
Defined benefit plan, one-time cash payment				6,000,000
Defined benefit pension plans, voluntary contributions	$ 6,000,000	$ 10,000,000	$ 0