EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator for basic and diluted earnings per share:
Net income	$ 50,255	$ 37,359	$ 114,673	$ 61,000
Numerator for basic and diluted earnings per share	$ 50,255	$ 37,359	$ 114,673	$ 61,000
Denominator:
Weighted average common shares for basic earnings per share	53,517,124	51,899,416	53,299,038	51,431,353
Effect of dilutive securities (in shares):
Net effect of dilutive stock options, restricted stock units and restricted stock awards	3,069,885	2,949,203	3,115,948	2,939,931
Weighted average common shares for diluted earnings per share	56,587,009	54,848,619	56,414,986	54,371,284
Net income per share:
Basic (in dollars per share)	$ 0.94	$ 0.72	$ 2.15	$ 1.19
Diluted (in dollars per share)	$ 0.89	$ 0.68	$ 2.03	$ 1.12
Anti-dilutive options not included in the calculation (in shares)	155,142	654,435	104,186	1,463,156