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Stockholders' Equity Stockholders' Equity (Four quarterly assumptions for fair value of the right (option) to purchase shares under ESPP) (Details) (Employee Stock Purchase Plan)
3 Months Ended 12 Months Ended
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2012
Sep. 30, 2012
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Employee Stock Purchase Plan
                             
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                              
Dividend yield                         0.60% 1.70% 0.00%
Expected volatility                         41.00% 32.00% 29.00%
Risk-free interest rate 0.15% 0.135% 0.12% 0.08% 0.12% 0.09% 0.06% 0.02% 0.29% 0.24% 0.19% 0.15%      
Expected life (years) 1 year 9 months 6 months 3 months 1 year 9 months 6 months 3 months 1 year 9 months 6 months 3 months