EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator for basic and diluted earnings per share:
Net income	$ 65,618	$ 42,634	$ 180,291	$ 103,634
Numerator for basic and diluted earnings per share	$ 65,618	$ 42,634	$ 180,291	$ 103,634
Denominator:
Weighted average common shares for basic earnings per share	53,851,865	52,545,155	53,485,339	51,806,700
Effect of dilutive securities (in shares):
Net effect of dilutive stock options, restricted stock units and restricted stock awards	3,111,002	2,683,626	3,114,299	2,854,496
Weighted average common shares for diluted earnings per share	56,962,867	55,228,781	56,599,638	54,661,196
Net income per share:
Basic (in dollars per share)	$ 1.22	$ 0.81	$ 3.37	$ 2.00
Diluted (in dollars per share)	$ 1.15	$ 0.77	$ 3.19	$ 1.90
Anti-dilutive options not included in the calculation (in shares)	157,316	606,047	121,896	1,177,453