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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Stock-Based Compensation (Details) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
Assumptions used to estimate the fair values of the stock options granted [Abstract]          
Risk-free interest rate     2.18%    
Expected term of option     6 years 3 months    
Expected stock price volatility     39.50%    
Expected dividend yield     0.00%    
Additional Disclosures [Abstract]          
Proceeds from stock option exercises     $ 2,133,396 $ 2,570,830  
Closing price of common stock (in dollars per share) $ 53.52   $ 53.52    
2019 Plan [Member]          
Share Based Compensation Expense [Abstract]          
Number of shares authorized for issuance (in shares) 1,248,848   1,248,848    
Number of shares available for issuance (in shares) 1,100,000   1,100,000    
Award expiry period     10 years    
2019 Plan [Member] | Minimum [Member]          
Share Based Compensation Expense [Abstract]          
Award vesting period     1 year    
2019 Plan [Member] | Maximum [Member]          
Share Based Compensation Expense [Abstract]          
Award vesting period     4 years    
2001 Plan [Member]          
Share Based Compensation Expense [Abstract]          
Number of shares available for issuance (in shares) 148,848   148,848    
Restricted Stock Awards [Member]          
Additional Disclosures [Abstract]          
Unrecognized compensation cost $ 460,000   $ 460,000    
Recognized compensation period     1 year 3 months    
Restricted Stock Awards [Member] | General and Administrative [Member]          
Additional Disclosures [Abstract]          
Stock-based compensation expense $ 146,000   $ 146,000    
Restricted Stock Awards [Member] | 2019 Plan [Member]          
Restricted Stock Awards [Roll Forward]          
Nonvested, Beginning balance (in shares)     0    
Issued (in shares)     9,950    
Vested (in shares)     0    
Forfeited (in shares)     0    
Nonvested, Ending balance (in shares) 9,950   9,950   0
Weighted-Average Grant Date Fair Value Per Share [Roll Forward]          
Nonvested, Beginning of period (in dollars per share)     $ 0    
Issued (in dollars per share)     60.85    
Vested (in dollars per share)     0    
Forfeited (in dollars per share)     0    
Nonvested, Ending of period (in dollars per share) $ 60.85   $ 60.85   $ 0
Stock Options [Member]          
Additional Disclosures [Abstract]          
Proceeds from stock option exercises     $ 2,100,000 2,600,000  
Unrecognized compensation cost $ 1,700,000   $ 1,700,000    
Recognized compensation period     3 years 22 days    
Stock Options [Member] | General and Administrative [Member]          
Additional Disclosures [Abstract]          
Stock-based compensation expense $ 114,000 $ 64,000 $ 374,000 $ 160,000  
Stock Options [Member] | 2001 Plan [Member]          
Stock Options Activity [Roll Forward]          
Outstanding, beginning of period (in shares)     175,500    
Grants (in shares)     10,000    
Exercised (in shares)     (73,063)    
Forfeitures (in shares)     (11,250)    
Outstanding, end of period (in shares) 101,187   101,187   175,500
Exercisable, end of period (in shares) 28,812   28,812    
Weighted Average Exercise Price [Roll Forward]          
Outstanding, beginning of period (in dollars per share)     $ 37.73    
Grants (in dollars per share)     66.40    
Exercised (in dollars per share)     29.20    
Forfeitures (in dollars per share)     41.82    
Outstanding, end of period (in dollars per share) $ 46.26   46.26   $ 37.73
Exercisable, end of period (in dollars per share) $ 21.74   $ 21.74    
Weighted Average Remaining Contractual Term [Roll Forward]          
Outstanding     7 years 7 months 17 days   6 years 3 months 29 days
Grants     0 years    
Exercised     0 years    
Forfeitures         0 years
Exercisable     3 years 11 months 16 days    
Aggregate Intrinsic Value [Roll Forward]          
Outstanding, beginning of period     $ 4,014,235    
Grants     0    
Exercised     2,229,195    
Forfeitures     0    
Outstanding, end of period $ 1,061,135   1,061,135   $ 4,014,235
Exercisable, end of period $ 915,593   $ 915,593