Share Based Compensation - Restricted Stock Awards (Details) - Restricted shares - $ / shares
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2018
Sep. 30, 2017
Avg wtd grant-date fair value      
Unvested at beginning of period   $ 11.82 $ 9.48
Granted   13.81 13.51
Vested   10.48 7.99
Forfeited     8.81
Unvested at end of period $ 13.18 $ 13.18 $ 11.82
Units      
Unvested at beginning of period   1,293,107 1,018,228
Granted (in shares)   1,904,595 623,165
Vested (in shares)   (209,765) (339,701)
Forfeited (in shares)     (8,585)
Unvested at end of period 2,987,937 2,987,937 1,293,107
2018 Plan      
Units      
Granted (in shares) 209,654 225,852  
Vested (in shares) (6,771)    
Director Plan      
Avg wtd grant-date fair value      
Unvested at beginning of period     $ 5.71
Vested     $ 5.71
Units      
Unvested at beginning of period     49,230
Vested (in shares)     (49,230)