NET INCOME PER SHARE (Details) - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 15, 2017	Jun. 15, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive potential common shares (in thousands of shares)	5,353	4,399	2,371
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive potential common shares (in thousands of shares)	2,290	3,670	1,901
Non-vested restricted stock units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive potential common shares (in thousands of shares)	3,063	729	470
Convertible Debt [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Long-term Debt, Gross				$ 123.0	$ 125.0