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Pension Plan - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
1 Months Ended 9 Months Ended
Jan. 31, 2012
Sep. 30, 2012
Dec. 31, 2011
Employee Benefit Plans [Line Items]      
Increase in fair value of qualified plan assets   $ 32.9  
Increased percent in fair value of qualified plan assets   34.30%  
Fair value of plan assets   128.6 95.7
Employer contributions to qualified plan $ 25.0