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CAPITAL STOCK AND SHARE-BASED COMPENSATION - Narrative (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Jun. 07, 2012
Jun. 06, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Common stock, authorized (shares) 60,000,000 60,000,000      
Common stock, par value (usd per share) $ 0.001 $ 0.001      
Preferred stock, authorized (shares) 5,000,000 5,000,000      
Preferred stock, par value (usd per share) $ 0.001 $ 0.001      
Common stock, issued (shares) 36,638,021 36,252,280      
Common stock, outstanding (shares) 32,284,051 31,973,505      
Preferred stock, issued (shares) 0 0      
Percentage of ownership in subsidiaries 50.00%        
Equity-based awards, number of shares authorized (shares) 2,500,000        
Equity-based awards, shares available for grant (shares) 2,000,000.0        
Percentage of total combined voting power of the Company and subsidiaries 10.00%        
Percentage of market value for purchases under Employee Stock Purchase Program (percent) 85.00%        
Common stock available for issuance under Employee Stock Purchase Plan (shares) 1,348,327        
Employee Stock Purchase Plan expense $ 0.6 $ 0.5 $ 0.4    
Options granted (shares) 142,122        
Tax benefit from stock option exercise $ 1.3 1.6 0.3    
Intrinsic value of options outstanding 102.7        
Intrinsic value of options exerciseable 78.2        
Intrinsic value of options exercised during the period $ 7.3 $ 9.7 $ 3.9    
Maximum [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Contractual term of share-based award ten        
Common stock available for issuance under Employee Stock Purchase Plan (shares)       4,500,000 2,500,000
Vesting period of equity-based awards 4 years        
Minimum [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period of equity-based awards 12 months        
Share-Based Awards [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Fair value of share of common stock (percent) 100.00%        
Share Based Awards to More Than Ten Percent Owner [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Fair value of share of common stock (percent) 110.00%        
Stock Option [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Options granted (shares) 142,122 163,666 308,292    
Stock compensation expense $ 6.2 $ 5.7 $ 5.6    
Unrecognized compensation expense $ 6.1        
Unrecognized compensation expense weighted-average period for recognitions (years) 1 year 9 months 18 days        
Non-Vested Stock [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock compensation expense $ 1.2 $ 1.4 $ 1.7    
Unrecognized compensation expense $ 0.8        
Unrecognized compensation expense weighted-average period for recognitions (years) 4 months 24 days        
Non-vested stock granted, weighted average grant date fair value (usd per share) $ 119.12 $ 80.54 $ 62.67    
Vesting period of equity-based awards 1 year        
Non-Vested Stock Units - Service-Based [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock compensation expense $ 8.7 $ 4.5 $ 3.6    
Unrecognized compensation expense $ 11.4        
Unrecognized compensation expense weighted-average period for recognitions (years) 1 year 10 months 24 days        
Non-vested stock granted, weighted average grant date fair value (usd per share) $ 123.70 $ 95.14 $ 53.79    
Non-Vested Stock Units - Service-Based and Performance-Based [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock compensation expense $ 8.4 $ 5.8 $ 5.0    
Unrecognized compensation expense $ 13.2        
Unrecognized compensation expense weighted-average period for recognitions (years) 2 years        
Non-vested stock granted, weighted average grant date fair value (usd per share) $ 128.89 $ 79.59 $ 52.99    
Performance-based award, target number of units to be received (shares) 102,585        
Additional Performance Based Award Target share Amount 18,327