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STOCKHOLDERS' EQUITY, Restricted Stock and Performance Share (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Weighted Average Assumptions [Abstract]    
Unrecognized compensation cost related to non-vested shares $ 11,860 $ 10,754
Weighted-average period of recognition for unrecognized compensation cost 2 years  
Estimated share-based compensation expense for current fiscal year $ 6,700  
Restricted Stock [Member]    
Non-vested restricted stock [Roll Forward]    
Non-vested balance as of beginning of period (in shares) 66 102
Granted (in shares) 37 9
Vested (in shares) (17) (41)
Forfeited (in shares) 0 (4)
Non-vested balance as of end of period (in shares) 86 66
Weighted average grant date fair value [Abstract]    
Non-vested balance as of beginning of period (in dollars per share) $ 65.66 $ 54.18
Granted (in dollars per share) 75.19 85.40
Vested (in dollars per share) 57.65 50.07
Forfeited (in dollars per share) 0 55.45
Non-vested balance as of end of period (in dollars per share) $ 71.40 $ 61.05
Performance Shares [Member]    
Non-vested restricted stock [Roll Forward]    
Non-vested balance as of beginning of period (in shares) 39 34
Granted (in shares) 32 16
Vested (in shares) (15) 0
Forfeited (in shares) 0 (7)
Non-vested balance as of end of period (in shares) 56 43
Weighted average grant date fair value [Abstract]    
Non-vested balance as of beginning of period (in dollars per share) $ 72.62 $ 61.06
Granted (in dollars per share) 71.27 93.85
Vested (in dollars per share) 58.78 0
Forfeited (in dollars per share) 0 69.18
Non-vested balance as of end of period (in dollars per share) $ 75.47 $ 72.26
Weighted Average Assumptions [Abstract]    
Risk-free interest rate 2.40% 1.50%
Dividend yield 0.50% 0.60%
Expected volatility 27.00% 32.00%
Initial TSR (10.50%) 8.20%
Cliff vest 100.00%