Annual report pursuant to Section 13 and 15(d)

Line of Credit - Additional Information (Detail)

Line of Credit - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended 1 Months Ended
Dec. 31, 2012
Mar. 13, 2013
Subsequent Event
Oct. 29, 2012
Ninth Amended and restated
Oct. 29, 2012
Eleventh Amendment
Mar. 13, 2013
Subsequent Event
Line of Credit Facility [Line Items]          
Revolving credit facility, maximum borrowing capacity     $ 60 $ 80  
Revolving credit facility, expiration date     Dec. 31, 2013 Dec. 31, 2014  
Revolving credit facility, interest rate description Amounts borrowed under our revolving line of credit bear interest, at our option, at either the prime lending rate established by JPMorgan Chase Bank        
Revolving credit facility, interest rate above LIBOR 1.50%        
Revolving credit facility, unused annual commitment fee 0.25%        
Total outstanding letters of credit   46.8      
Revolving credit facility, amount outstanding   10      
Revolving credit facility, unused portion   23.2      
Line of credit covenant, current ratio         1.25
Line of credit covenant, debt to net worth         0.5
Line of credit covenant, Earnings before interest, taxes, depreciation and amortization (EBITDA) to interest expense ratio   4.0      
Line of credit covenant, minimum net worth required   $ 241.2