EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator for common earnings per share:
Net income	$ 22,873	$ 19,040	$ 56,818	$ 51,218
Numerator for basic and diluted earnings per share	$ 22,873	$ 19,040	$ 56,818	$ 51,218
Denominator for basic earnings per share:
Weighted average common shares outstanding (in shares)	49,043	47,315	48,506	47,058
Effect of dilutive securities (in shares):
Stock options, RSUs and performance-based awards (in shares)	3,301	2,514	3,249	2,472
Denominator for diluted earnings per share (in shares)	52,344	49,829	51,755	49,530
Net income per share:
Basic (in dollars per share)	$ 0.47	$ 0.40	$ 1.17	$ 1.09
Diluted (in dollars per share)	$ 0.44	$ 0.38	$ 1.10	$ 1.03
Anti-dilutive options not included in the calculation (in shares)	2,143	2,691	1,456	2,152