Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plan - Additional Information (Detail)

v2.4.0.6
Employee Benefit Plan - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]      
Plan contributions cost $ 2.8 $ 2.4 $ 2.4
Employee vested percentage 100.00%    
Participation waiting period 30 days    
First 4 percent of employees pre-tax contributions [Member]
      
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]      
Employee vested percentage 100.00%    
Next 2 percent of employees pre-tax contributions [Member]
      
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]      
Employee vested percentage 50.00%