Pensions and Other Postretirement Benefits - Additional Information (Detail) (Immaterial correction of an error, USD $)
In Thousands, unless otherwise specified
9 Months Ended 12 Months Ended
Sep. 30, 2012
Dec. 31, 2011
Immaterial correction of an error
   
Correction in amortization period 10 years  
Average remaining life expectancy of plan participants 26 years  
Pre-tax benefit related to the reversal of amortization   $ 2,000