SHAREHOLDERS' EQUITY AND SHARE-BASED COMPENSATION - Stock option information (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Options outstanding
Number (in shares) | shares	1,745,906
Options exercisable
Number (in shares) | shares	1,140,333
Up to $10.00
Stock options outstanding and exercisable
Exercise price, low end of range (in dollars per share)	$ 0.00	[1]
Exercise price, high end of range (in dollars per share)	$ 10.00	[1]
Options outstanding
Number (in shares) | shares	286,252
Weighted average remaining contractual life (in years)	6 months 11 days
Weighted average exercise price (in dollars per share)	$ 9.14
Options exercisable
Number (in shares) | shares	286,252
Weighted average remaining contractual life (in years)	6 months 11 days
Weighted average exercise price (in dollars per share)	$ 9.14
$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	246,479
Weighted average remaining contractual life (in years)	7 years 3 months 7 days
Weighted average exercise price (in dollars per share)	$ 18.79
Options exercisable
Number (in shares) | shares	163,424
Weighted average remaining contractual life (in years)	7 years 3 months
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	813,730
Weighted average remaining contractual life (in years)	4 years 10 months 10 days
Weighted average exercise price (in dollars per share)	$ 25.11
Options exercisable
Number (in shares) | shares	559,576
Weighted average remaining contractual life (in years)	3 years 2 months 16 days
Weighted average exercise price (in dollars per share)	$ 24.11
$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	224,695
Weighted average remaining contractual life (in years)	8 years 11 days
Weighted average exercise price (in dollars per share)	$ 36.27
Options exercisable
Number (in shares) | shares	53,924
Weighted average remaining contractual life (in years)	4 years 9 months 11 days
Weighted average exercise price (in dollars per share)	$ 32.67
$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)	4 years 2 months 9 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)	4 years 2 months 9 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)	6 years 10 months 10 days
Weighted average exercise price (in dollars per share)	$ 72.78
Options exercisable
Number (in shares) | shares	4,688
Weighted average remaining contractual life (in years)	6 years 10 months 10 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	30,000
Weighted average remaining contractual life (in years)	6 years 4 months 6 days
Weighted average exercise price (in dollars per share)	$ 86.22
Options exercisable
Number (in shares) | shares	8,438
Weighted average remaining contractual life (in years)	5 years 11 months 9 days
Weighted average exercise price (in dollars per share)	$ 85.43
$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)	6 years 1 month 24 days
Weighted average exercise price (in dollars per share)	$ 95.64
Options exercisable
Number (in shares) | shares	11,250
Weighted average remaining contractual life (in years)	5 years 11 months 12 days
Weighted average exercise price (in dollars per share)	$ 95.38
$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)	6 years 4 months 13 days
Weighted average exercise price (in dollars per share)	$ 105.11
Options exercisable
Number (in shares) | shares	1,406
Weighted average remaining contractual life (in years)	6 years 4 months 13 days
Weighted average exercise price (in dollars per share)	$ 105.11

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