STOCK-BASED PLANS (Summary of Stock Option Activity) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 09, 2010
Stock-based plans
Shares of common stock reserved for issuance (in shares)				3,698,050
Stock based compensation expense	$ 12,128,000	$ 7,385,000	$ 6,707,000
Stock Options
Stock options outstanding at the beginning of the period (in shares)	783,182	1,176,640	1,086,040
Granted (in shares)	265,000	58,000	162,100
Exercised (in shares)	(183,592)	(395,482)	(3,000)
Forfeited (in shares)	(46,592)	(54,976)	(68,500)
Expired (in shares)	0	(1,000)	0
Stock options outstanding at the end of the period (in shares)	817,998	783,182	1,176,640
Stock options exercisable at the end of the period (in shares)	268,298
Remaining unvested options outstanding and expected to vest (in shares)	797,320
Weighted Average Exercise Price
Stock options outstanding at the beginning of the period (in dollars per share)	$ 90.22	$ 78.87	$ 77.11
Granted (in dollars per share)	124.56	119.85	109.42
Exercised (in dollars per share)	65.72	58.81	60.33
Forfeited (in dollars per share)	121.34	105.17	122.93
Expired (in dollars per share)	0.00	57.77	0.00
Stock options outstanding at the end of the period (in dollars per share)	105.06	$ 90.22	$ 78.87
Stock options exercisable at the end of the period (in dollars per share)	67.82
Stock options expected to vest at the end of the period (in dollars per share)	$ 104.61
Weighted average remaining contractual term of stock options outstanding	6 years 4 months
Weighted average remaining contractual term of stock options exercisable	2 years 11 months 20 days
Weighted average remaining contractual term of stock options expected to vest	6 years 3 months 8 days
Aggregate intrinsic value	$ 8,608,841
Aggregate intrinsic value of stock options exercisable	8,524,841
Aggregate intrinsic value of stock options expected to vest	$ 8,607,055
Maximum
Stock-based plans
Maximum number of shares available for future grant	2,199,894
Stock Options
Stock-based plans
Stock based compensation expense	$ 12,100,000	$ 8,400,000	$ 9,400,000
Share based compensation costs capitalized	$ 2,400,000	$ 1,100,000	$ 2,600,000
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 105.06
Number Outstanding (in shares)	817,998
Weighted Average Remaining Contractual Term	6 years 4 months
Number Exercisable (in shares)	268,298
Significant assumptions used in Black-Scholes option-pricing model
Weighted average grant date fair value (in dollars per share)	$ 48.27	$ 34.51	$ 36.55
Weighted-average expected life of options	8 years 4 months 24 days	8 years 4 months 24 days	7 years 4 months 24 days
Weighted-average risk-free interest rate (as a percent)	2.70%	2.20%	1.80%
Weighted-average expected volatility (as a percent)	24.70%	22.80%	33.10%
Expected annual dividend per share	$ 0.00	$ 0.00	$ 0.00
Expiration period	10 years
Unamortized stock option expense	$ 15,300,000
Weighted-average period for recognition of unamortized stock expense	5 years 1 month
Stock Options | Minimum
Significant assumptions used in Black-Scholes option-pricing model
Exercisable period	5 years
Stock Options | General and Administrative Expense
Stock-based plans
Stock based compensation expense	$ 2,200,000	$ 1,600,000	$ 2,900,000
Stock Options | $46.49 - 55.82
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 49.93
Number Outstanding (in shares)	11,100
Weighted Average Remaining Contractual Term	2 years 9 months 12 days
Number Exercisable (in shares)	11,100
Stock Options | $46.49 - 55.82 | Minimum
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 46.46
Stock Options | $46.49 - 55.82 | Maximum
Exercise price range of stock options
Exercise Price (in dollars per share)	55.82
Stock Options | $57.77 - 60.33
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 57.99
Number Outstanding (in shares)	162,401
Weighted Average Remaining Contractual Term	2 years 3 months 5 days
Number Exercisable (in shares)	162,401
Stock Options | $57.77 - 60.33 | Minimum
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 57.77
Stock Options | $57.77 - 60.33 | Maximum
Exercise price range of stock options
Exercise Price (in dollars per share)	60.33
Stock Options | $61.64 - 69.75
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 66.65
Number Outstanding (in shares)	49,129
Weighted Average Remaining Contractual Term	3 years 4 months 24 days
Number Exercisable (in shares)	49,129
Stock Options | $61.64 - 69.75 | Minimum
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 61.64
Stock Options | $61.64 - 69.75 | Maximum
Exercise price range of stock options
Exercise Price (in dollars per share)	69.75
Stock Options | $81.80 - 110.50
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 101.69
Number Outstanding (in shares)	68,960
Weighted Average Remaining Contractual Term	6 years 1 month 29 days
Number Exercisable (in shares)	38,960
Stock Options | $81.80 - 110.50 | Minimum
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 81.80
Stock Options | $81.80 - 110.50 | Maximum
Exercise price range of stock options
Exercise Price (in dollars per share)	110.50
Stock Options | $112.64 - 151.72
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 124.77
Number Outstanding (in shares)	526,408
Weighted Average Remaining Contractual Term	8 years
Number Exercisable (in shares)	6,708
Stock Options | $112.64 - 151.72 | Minimum
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 112.64
Stock Options | $112.64 - 151.72 | Maximum
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 151.72