Share Based Compensation - Restricted Stock Awards (Details) - Restricted shares - $ / shares
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2019
Jun. 30, 2018
Avg wtd grant-date fair value      
Unvested at beginning of period   $ 13.17 $ 11.82
Granted $ 17.17 16.02 14.24
Vested   13.41 11.96
Forfeited   14.02  
Unvested at end of period $ 13.87 $ 13.87 $ 13.20
Units      
Unvested at beginning of period   2,997,856 1,293,107
Granted (in shares) 477,284 995,669 1,694,941
Vested (in shares) (4,360) (43,996) (33,028)
Forfeited (in shares)   (367,998)  
Unvested at end of period 3,581,531 3,581,531 2,955,020