Annual report pursuant to Section 13 and 15(d)

STOCK???BASED COMPENSATION - Additional Information (Details)

v3.10.0.1
STOCK‑BASED COMPENSATION - Additional Information (Details)
12 Months Ended 22 Months Ended
Mar. 22, 2017
shares
Mar. 16, 2017
USD ($)
installment
shares
Jul. 19, 2016
installment
shares
Dec. 31, 2014
Dec. 01, 2013
installment
shares
Sep. 30, 2013
$ / shares
shares
Jun. 14, 2013
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
Dec. 31, 2016
USD ($)
$ / shares
Dec. 31, 2014
$ / shares
shares
Mar. 31, 2017
shares
Mar. 04, 2014
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Options granted (in shares)               0          
Outstanding value of options (in dollars per share) | $ / shares               $ 0.00          
Forfeited (in shares)               29,255          
Deferred IPO Bonus | $               $ 2,809,000 $ 8,405,000        
Granted (in dollars per share) | $ / shares               $ 0.00 $ 3.35 $ 1.77      
Options, outstanding, intrinsic value | $               $ 34,000,000          
Options, exercisable, intrinsic value | $               34,000,000          
Options, exercises in period, intrinsic value | $               $ 700,000          
Options, outstanding, weighted average remaining contractual term               5 years 10 months 13 days          
Options, exercisable, weighted average remaining contractual term               5 years 6 months 29 days          
Common stock, par value (in dollars per share) | $ / shares           $ 0.001   $ 0.001 $ 0.001        
Non-vested restricted stock units                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Granted (in dollars per share) | $ / shares           $ 3.89              
Target Shares Granted (in shares) 372,335         372,335   319,250          
Restricted stock units, conversion of stock, conversion rights (in shares)           1              
Performance stock units                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Target Shares Granted (in shares)               178,975          
Stock Option Plan                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Number of shares authorized (in shares)                         4,645,884
Stock Option Plan | Stock options                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Options granted (in shares)                     3,499,228    
Outstanding value of options (in dollars per share) | $ / shares                     $ 3.96    
Expiration period       10 years                  
Incentive Award Plan                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Number of shares authorized (in shares)                       5,800,000  
Compensation cost not yet recognized, period for recognition               1 year 11 months 19 days          
Tax benefit from compensation expense | $               $ 5,500,000 $ 9,500,000 $ 1,600,000      
Compensation not yet recognized, stock options | $               11,500,000          
Incentive Award Plan | Non-vested restricted stock units                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Stock-based compensation | $               $ 2,900,000 6,168,081.03 0      
Target Shares Granted (in shares)               319,250          
Restricted stock units, conversion of stock, conversion rights (in shares)               1          
Compensation not yet recognized, other than options | $               $ 5,700,000          
Compensation cost not yet recognized, period for recognition               1 year 7 months 6 days          
Incentive Award Plan | Performance stock units                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Stock-based compensation | $               $ 2,000,000 400,000 0      
June 14, 2013 | Stock Option Plan | Stock options                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Options granted (in shares)             2,799,408            
Expiration period             10 years            
Award vesting rights             25.00%            
December 1, 2013 | Stock Option Plan | Stock options                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Options granted (in shares)         699,820                
Expiration period         10 years                
Forfeited (in shares)               114,456          
Deferred IPO Bonus | $   $ 5,100,000                      
Number of installments | installment         4                
July 19, 2016 | Stock Option Plan | Stock options                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Options granted (in shares)     1,274,549                    
Expiration period     10 years                    
Number of installments | installment     5                    
March 16, 2017 | Stock Option Plan | Stock options                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Options granted (in shares)   793,738                      
Expiration period   10 years                      
Stock-based compensation | $               $ 600,000 $ 2,909,790.12 $ 1,649,282.42      
Number of installments | installment   4