Annual report pursuant to Section 13 and 15(d)

Stock Compensation (Details Textual)

v2.4.0.6
Stock Compensation (Details Textual) (USD $)
In Millions, except Share data, unless otherwise specified
 12 Months Ended 12 Months Ended
Dec. 31, 2011
Y
Dec. 31, 2010
Y
Dec. 31, 2009
Apr. 16, 2007
Jul. 01, 1998
Apr. 16, 2007
Employee Stock Purchase Plan 1998 [Member]
Jul. 01, 1998
Employee Stock Purchase Plan 1998 [Member]
Dec. 31, 2011
Class A
Dec. 31, 2010
Class A
Dec. 31, 2009
Class A
May 31, 2003
Class A
Jun. 30, 2001
Class A
Stock Compensation (Textual) [Abstract]                        
Number of shares authorized for issuance                     11,215,154 8,215,154
Unrecognized compensation cost related to unvested stock $ 11.3 $ 25.1                    
Weighted Average Period for Recognition Of Cost 0.9 1.9                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Number of shares reserved for issuance       7,500,000   3,000,000 2,781,415          
Number of shares reserved for issuance       7,500,000   3,000,000 2,781,415          
Expiration period of stock option awards 10                      
Stock options granted 0 0 0                  
Vesting period stock option awards 3 years                      
Intrinsic value of options exercised 1.2 20.9 1.3                  
Number of shares remain available for grant 5,116,881                      
Unrecognized compensation cost related to unvested stock 11.3 25.1                    
Weighted Average Period for Recognition Of Cost 0.9 1.9                    
Total fair value of shares vested 13.9 14.4                    
Period utilized to implement employee stock purchase plan 6 months                      
Interval for purchases occurring 6 months                      
Eligibility to Participate Stock Purchase Plan Atleast 20 hours per week and more than five months in calendar year                      
Proceeds from issuance of common stock under the employee stock purchase plan, shares 178,189 103,430 189,428         178,000 103,000 190,000    
Proceeds from issuance of common stock under the employee stock purchase plan $ 2.0 $ 2.1 $ 1.6                  
Maximum percentage of employee's compensation to purchase common stock       15.00% 15.00%              
Percentage of price of common stock purchased       85.00% 85.00%