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STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS - Stock Option and Restricted Stock Plans (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2016
Mar. 31, 2016
Dec. 31, 2015
Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share based compensation, shares authorized (in shares)     15,825,223          
Share based compensation, shares authorized for future grant (in shares)     3,938,916          
Excess tax benefits recognized within income tax expense     $ 500          
Excess tax benefits relating to stock-based compensation         $ 590   $ 413  
Proceeds from employee common stock purchases     $ 1,330   1,114   1,131  
Service-based Restricted Shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share based compensation, award shares granted in period (in shares)     292,448          
Forfeited shares (in shares)     47,661          
Share based compensation, fair value of restricted stock vested     $ 4,700   $ 4,600   $ 4,700  
Granted (in usd per share)     $ 21.46   $ 17.67   $ 16.69  
Intrinsic value of nonvested restricted stock awards expected to vest     $ 11,200          
Unrecognized compensation related to non-vested awards     $ 8,200          
Unrecognized compensation costs, weighted average period expected to be recognized (years)     2 years          
Performance- based Restricted Shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share based compensation, award shares granted in period (in shares)     110,678          
Share based compensation, annual award vesting period from date of grant     3 years   3 years   3 years  
Forfeited shares (in shares)     21,503          
Share based compensation, fair value of restricted stock vested     $ 1,200   $ 1,600   $ 800  
Granted (in usd per share)     $ 22.00   $ 17.62   $ 17.11  
Performance Period 2014 to 2016 | Performance- based Restricted Shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share based compensation, performance-based restricted stock awards, grant date         Feb. 24, 2014      
Share based compensation, award shares earned in period (in shares)         59,437      
Share based compensation, dividend earned on shares subject to the awards (in shares)         4,945      
Forfeited shares (in shares)         21,503      
Performance Period 2013 to 2015 | Performance- based Restricted Shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share based compensation, performance-based restricted stock awards, grant date             Feb. 05, 2013  
Share based compensation, award shares earned in period (in shares)             96,732  
Share based compensation, dividend earned on shares subject to the awards (in shares)             6,990  
Forfeited shares (in shares)             18,964  
Employees And Executives | Service Based Awards | Service-based Restricted Shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share based compensation, award shares granted in period (in shares)     250,039          
Share based compensation, award granted in period grant-date fair value     $ 5,400          
Share based compensation, annual award vesting period from date of grant     1 year          
Employees And Executives | Service Based Awards | Service-based Restricted Shares | Share-based Compensation Award, Tranche One                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share based compensation, award annual installment vesting rate     25.00%          
Employees And Executives | Performance Based Awards | Service-based Restricted Shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share based compensation, award shares granted in period (in shares)   110,678            
Share based compensation, award granted in period grant-date fair value   $ 2,400            
Share based compensation, annual award vesting period from date of grant   3 years            
Non Employee Directors | Service Based Awards | Service-based Restricted Shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share based compensation, award shares granted in period (in shares)     37,464          
Share based compensation, award granted in period grant-date fair value     $ 800          
Share based compensation, annual award vesting period from date of grant     1 year          
Employee Stock                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share based compensation, shares authorized (in shares)     2,321,688          
Proceeds from employee common stock purchases       $ 1,300   $ 1,100   $ 1,100
Scenario, Forecast | Performance- based Restricted Shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Forfeited shares (in shares) 91,820