Stock-Based Compensation (Details 2) (Restricted stock units)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Restricted stock units
   
Restricted stock units    
Restricted stock units at the beginning of the period (in shares) 368,084 539,106
Shares awarded 170,994 131,597
Shares vested (231,969) (298,791)
Shares forfeited (11,082) (2,428)
Restricted stock units at the end of the period (in shares) 296,027 369,484
Outstanding restricted shares vesting schedule    
Outstanding restricted stock unit awards, vesting in 2015 (in shares) 17,526  
Outstanding restricted stock unit awards, vesting in 2016 (in shares) 131,675  
Outstanding restricted stock unit awards, vesting in 2017 (in shares) 92,556  
Outstanding restricted stock unit awards, vesting in 2018 (in shares) 54,270