Employee Benefit Plans - Restricted Stock Activity (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Employee Benefit Plans      
Compensation cost $ 7,400 $ 9,000 $ 9,000
Restricted stock      
Employee Benefit Plans      
Compensation cost 966 335 88
Unrecognized compensation cost $ 3,900 $ 208 $ 43
Period for recognition 3 years    
Shares      
Unvested restricted stock, beginning balance (in shares) 234,744    
Granted (in shares) 2,347,347    
Vested (in shares) (234,744)    
Unvested restricted stock, end balance (in shares) 2,347,347 234,744  
Aggregate Intrinsic Value      
Unvested restricted stock aggregate intrinsic value $ 2,911    
Restricted stock | Minimum      
Employee Benefit Plans      
Vesting period 1 year    
Restricted stock | Maximum      
Employee Benefit Plans      
Vesting period 3 years