STOCK-BASED PLANS (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Nov. 09, 2010
Stock Options
Shares of common stock reserved for issuance				3,698,050
Maximum number of shares available for future grant	2,318,033
Stock options outstanding at the beginning of the period (in shares)	1,046,490	965,440	861,940
Granted (in shares)	117,000	116,500	132,100
Forfeited (in shares)	(77,450)	(35,450)	(28,600)
Stock options outstanding at the end of the period (in shares)	1,086,040	1,046,490	965,440
Stock options exercisable at the end of the period (in shares)	3,400
Remaining unvested options outstanding and expected to vest (in shares)	1,071,365
Weighted Average Exercise Price
Stock options outstanding at the beginning of the period (in dollars per share)	$ 72.61	$ 64.57	$ 59.17
Granted (in dollars per share)	134.24	144.26	99.38
Forfeited (in dollars per share)	103.84	87.45	62.40
Stock options outstanding at the end of the period (in dollars per share)	77.11	$ 72.61	$ 64.57
Stock options exercisable at the end of the period (in dollars per share)	60.03
Stock options expected to vest at the end of the period (in dollars per share)	$ 76.68
Weighted average remaining contractual term of stock options outstanding	6 years 3 months 18 days
Weighted average remaining contractual term of stock options exercisable	4 years 2 months 12 days
Weighted average remaining contractual term of stock options expected to vest	4 years 2 months 12 days
Aggregate intrinsic value	$ 43,927,338
Aggregate intrinsic value of stock options exercisable	180,646
Aggregate intrinsic value of stock options expected to vest	$ 43,679,612
Significant assumptions used in Black-Scholes option-pricing model
Expiration period	10 years
Stock based compensation expense	$ 7,284,000	$ 8,200,000	$ 5,782,000
Minimum
Significant assumptions used in Black-Scholes option-pricing model
Exercisable period	5 years
Stock Options
Stock Options
Share based compensation costs capitalized	$ 2,500,000	$ 0	$ 0
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 77.11
Number Outstanding (in shares)	1,086,040
Weighted Average Remaining Contractual Term	6 years 2 months 12 days
Number Exercisable (in shares)	3,400
Significant assumptions used in Black-Scholes option-pricing model
Weighted average grant date fair value (in dollars per share)	$ 44.45	$ 48.65	$ 28.04
Weighted-average expected life of options	7 years 6 months	7 years 6 months	7 years 3 months 18 days
Weighted-average risk-free interest rate (as a percent)	2.00%	2.20%	1.80%
Weighted-average expected volatility (as a percent)	26.10%	25.70%	22.00%
Unamortized stock option expense	$ 11,100,000
Stock based compensation expense	9,800,000	$ 8,200,000	$ 5,700,000
Stock Options | General and Administrative Expense
Significant assumptions used in Black-Scholes option-pricing model
Stock based compensation expense	$ 2,600,000	$ 4,300,000	$ 3,500,000
Stock Options | $46.49 - 55.82
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 52.74
Number Outstanding (in shares)	48,500
Weighted Average Remaining Contractual Term	5 years 7 months 6 days
Stock Options | $46.49 - 55.82 | Minimum
Exercise price range of stock options
Exercise Price (in dollars per share)	$ 46.49
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)	$ 57.94
Number Outstanding (in shares)	569,400
Weighted Average Remaining Contractual Term	5 years 2 months 12 days
Number Exercisable (in shares)	3,400
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)	$ 66.17
Number Outstanding (in shares)	169,240
Weighted Average Remaining Contractual Term	6 years 2 months 12 days
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)	$ 98.35
Number Outstanding (in shares)	107,400
Weighted Average Remaining Contractual Term	7 years 4 months 24 days
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)	$ 138.05
Number Outstanding (in shares)	191,500
Weighted Average Remaining Contractual Term	9 years
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