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STOCK PLANS (Textual) (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Apr. 23, 2015
Stock Plans        
Common shares available for future grant under all plans (in shares) 3,710,464      
Total stock-based compensation expense $ 18,554,000 $ 12,698,000 $ 10,332,000  
Tax benefit related to stock-based compensation recognized in the period 4,632,000 4,861,000 3,955,000  
Total unrecognized stock-based compensation expense related to nonvested stock options, restricted shares and restricted stock units $ 21,223,000      
Weighted average period of recognition of unrecognized stock-based compensation expense (in months) 2 years      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value $ 3,511,000 3,040,000 2,865,000  
Stock options        
Stock Plans        
Award expiration (in years) 10 years      
Award vesting period (in years) 3 years      
Aggregate intrinsic value of awards outstanding $ 22,411,000      
Aggregate intrinsic value of awards exercisable 23,714,000      
Total intrinsic value of awards exercised $ 4,779,000 $ 19,328,000 $ 30,967,000  
Restricted stock awards        
Stock Plans        
Shares converted (in shares) 32,922      
Shares granted 1,662      
Shares granted (in dollars per share) $ 91.02      
Remaining weighted average life of non-vested restricted awards (in years) 1 year      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number 12,438 47,856    
Restricted Stock Units        
Stock Plans        
Shares converted (in shares) 49,653      
Shares granted 148,833      
Shares granted (in dollars per share) $ 89.51      
Remaining weighted average life of non-vested restricted awards (in years) 1 year 4 months 24 days      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number 506,030 418,966    
Performance Shares [Member]        
Stock Plans        
Award vesting period (in years) 3 years      
Shares granted 31,760      
Shares granted (in dollars per share) $ 76.20      
Remaining weighted average life of non-vested restricted awards (in years) 1 year      
1995 Lincoln Stock Purchase Plan        
Stock Plans        
Maximum additional number of the Company's common shares that may be granted (in shares) 800,000      
Shares purchased (in shares) 8,324 10,458 15,827  
Equity and Incentive Compensation Plan [Member]        
Stock Plans        
Maximum additional number of the Company's common shares that may be granted (in shares)       5,400,000
Equity and Incentive Compensation Plan [Member] | Restricted Stock Units        
Stock Plans        
Shares granted 117,073      
Equity and Incentive Compensation Plan [Member] | Performance Shares [Member]        
Stock Plans        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number 107,045      
Director Plan        
Stock Plans        
Maximum additional number of the Company's common shares that may be granted (in shares)       300,000
2005 Plan | Restricted Stock Units        
Stock Plans        
Shares converted (in shares) 1,980      
Deferred RSUs (in shares) 99,801      
Minimum | Restricted stock awards        
Stock Plans        
Award vesting period (in years) 1 year      
Minimum | Restricted Stock Units        
Stock Plans        
Award vesting period (in years) 3 years      
Maximum | Restricted stock awards        
Stock Plans        
Award vesting period (in years) 3 years      
Maximum | Restricted Stock Units        
Stock Plans        
Award vesting period (in years) 5 years      
Maximum | 1995 Lincoln Stock Purchase Plan        
Stock Plans        
Dollar value of shares that each employee has the ability to purchase on the open market, on a commission-free basis annually under the plan $ 10,000