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Cash and stock-based compensation plans (Details 3) (USD $)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free rate Maximum   1.34%  
Stock Purchase Options [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average fair value per option $ 0 $ 3.01 $ 2.92
Weighted average expected term, in years 0 years 5 years 6 months 5 years 6 months
Expected volatility 0.00% 33.35% 30.00%
Risk-free rate 0.00%   2.52%
Risk-free rate Minimum   0.18%  
Expected dividend 0.00% 5.30% 4.50%