EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator for basic and diluted earnings per share:
Net income	$ 42,634	$ 26,174	$ 103,634	$ 74,503
Numerator for basic and diluted earnings per share	$ 42,634	$ 26,174	$ 103,634	$ 74,503
Denominator:
Weighted average common shares for basic earnings per share	52,545	51,131	51,807	50,172
Effect of dilutive securities (in shares):
Net effect of dilutive stock options, restricted stock units and restricted stock awards	2,684	2,733	2,855	2,987
Weighted average common shares for diluted earnings per share	55,229	53,864	54,662	53,159
Net income per share:
Basic (in dollars per share)	$ 0.81	$ 0.51	$ 2.00	$ 1.48
Diluted (in dollars per share)	$ 0.77	$ 0.49	$ 1.90	$ 1.40
Anti-dilutive options not included in the calculation (in shares)	606	2,357	1,177	2,324