Annual report pursuant to Section 13 and 15(d)

Share-Based Compensation and Employee Benefit Plans Share-Based Compensation and Employee Benefit Plans (Details 5)

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Share-Based Compensation and Employee Benefit Plans Share-Based Compensation and Employee Benefit Plans (Details 5) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
401 (K) Plan [Abstract]      
Maximum percentage of compensation employees can contribute to the 401K plan 90.00%    
Minimum age of participants who are eligible to contribute an additional portion of their annual compensation 50 years    
Employer matching contribution for the first 1% of the participants' eligible compensation (as a percent) 100.00%    
Maximum percentage of participants' compensation eligible for 100% employer matching contribution (as a percent) 1.00%    
Employer matching contribution for the next 5% after first 1% of the participants' eligible compensation (as a percent) 50.00%    
Maximum percentage of participants' compensation eligible for 50% employer matching contribution (as a percent) 5.00%    
Employer's aggregate matching contribution for the first 6% of the participants' eligible compensation (as a percent) 3.50%    
Maximum percentage of participants' compensation eligible for 3.5% aggregate employer matching contribution 6.00%    
Participants' vesting portion in employer matching contribution after one year of credited service (as a percent) 50.00%    
Period of credited service after which participants are 50% vested in employer matching contribution 1 year    
Participants' vesting portion in employer matching contribution after two years of credited service (as a percent) 100.00%    
Period of credited service after which participants are 100% vested in employer matching contribution 2 years    
Matching contribution under the plan $ 1.1 $ 1.1 $ 1.0