SHAREHOLDERS' EQUITY AND SHARE-BASED COMPENSATION - Stock option information (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Options outstanding
Number (in shares) | shares	1,440,566
Options exercisable
Number (in shares) | shares	874,304
$10.01 — $20.00
Stock options outstanding and exercisable
Exercise price, low end of range (in dollars per share)	$ 10.01	[1]
Exercise price, high end of range (in dollars per share)	$ 20.00	[1]
Options outstanding
Number (in shares) | shares	212,667
Weighted average remaining contractual life (in years)	6 years 21 days
Weighted average exercise price (in dollars per share)	$ 18.79
Options exercisable
Number (in shares) | shares	203,344
Weighted average remaining contractual life (in years)	6 years 18 days
Weighted average exercise price (in dollars per share)	$ 18.79
$20.01 — $30.00
Stock options outstanding and exercisable
Exercise price, low end of range (in dollars per share)	20.01	[1]
Exercise price, high end of range (in dollars per share)	$ 30.00	[1]
Options outstanding
Number (in shares) | shares	925,563
Weighted average remaining contractual life (in years)	4 years 9 months 14 days
Weighted average exercise price (in dollars per share)	$ 24.60
Options exercisable
Number (in shares) | shares	537,607
Weighted average remaining contractual life (in years)	2 years 25 days
Weighted average exercise price (in dollars per share)	$ 23.81
$30.01 — $40.00
Stock options outstanding and exercisable
Exercise price, low end of range (in dollars per share)	30.01	[1]
Exercise price, high end of range (in dollars per share)	$ 40.00	[1]
Options outstanding
Number (in shares) | shares	132,586
Weighted average remaining contractual life (in years)	6 years 2 months 12 days
Weighted average exercise price (in dollars per share)	$ 34.63
Options exercisable
Number (in shares) | shares	54,478
Weighted average remaining contractual life (in years)	3 years 6 months 14 days
Weighted average exercise price (in dollars per share)	$ 32.82
$60.01 — $70.00
Stock options outstanding and exercisable
Exercise price, low end of range (in dollars per share)	60.01	[1]
Exercise price, high end of range (in dollars per share)	$ 70.00	[1]
Options outstanding
Number (in shares) | shares	71,000
Weighted average remaining contractual life (in years)	3 years 2 months 8 days
Weighted average exercise price (in dollars per share)	$ 60.73
Options exercisable
Number (in shares) | shares	51,375
Weighted average remaining contractual life (in years)	3 years 2 months 8 days
Weighted average exercise price (in dollars per share)	$ 60.74
$70.01 — $80.00
Stock options outstanding and exercisable
Exercise price, low end of range (in dollars per share)	70.01	[1]
Exercise price, high end of range (in dollars per share)	$ 80.00	[1]
Options outstanding
Number (in shares) | shares	25,000
Weighted average remaining contractual life (in years)	4 years 6 months 3 days
Weighted average exercise price (in dollars per share)	$ 72.78
Options exercisable
Number (in shares) | shares	6,250
Weighted average remaining contractual life (in years)	5 months 12 days
Weighted average exercise price (in dollars per share)	$ 72.78
$80.01 — $90.00
Stock options outstanding and exercisable
Exercise price, low end of range (in dollars per share)	80.01	[1]
Exercise price, high end of range (in dollars per share)	$ 90.00	[1]
Options outstanding
Number (in shares) | shares	25,000
Weighted average remaining contractual life (in years)	5 years 7 months 6 days
Weighted average exercise price (in dollars per share)	$ 86.69
Options exercisable
Number (in shares) | shares	6,250
Weighted average remaining contractual life (in years)	5 years 7 months 6 days
Weighted average exercise price (in dollars per share)	$ 86.69
$90.01 — $100.00
Stock options outstanding and exercisable
Exercise price, low end of range (in dollars per share)	90.01	[1]
Exercise price, high end of range (in dollars per share)	$ 100.00	[1]
Options outstanding
Number (in shares) | shares	46,875
Weighted average remaining contractual life (in years)	5 years
Weighted average exercise price (in dollars per share)	$ 95.64
Options exercisable
Number (in shares) | shares	13,125
Weighted average remaining contractual life (in years)	4 years 6 months 3 days
Weighted average exercise price (in dollars per share)	$ 95.59
$100.01 — $110.00
Stock options outstanding and exercisable
Exercise price, low end of range (in dollars per share)	100.01	[1]
Exercise price, high end of range (in dollars per share)	$ 110.00	[1]
Options outstanding
Number (in shares) | shares	1,875
Weighted average remaining contractual life (in years)	5 months 12 days
Weighted average exercise price (in dollars per share)	$ 105.11
Options exercisable
Number (in shares) | shares	1,875
Weighted average remaining contractual life (in years)	5 months 12 days
Weighted average exercise price (in dollars per share)	$ 105.11

[1] These options contain market-based and performance-based components as described above.