EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator for basic and diluted earnings per share:
Net income	$ 58,777	$ 60,754	$ 50,255	$ 64,418	$ 119,531	$ 114,673
Numerator for basic and diluted earnings per share	$ 58,777		$ 50,255		$ 119,531	$ 114,673
Denominator:
Weighted average common shares for basic earnings per share	54,681,959		53,517,124		54,464,753	53,299,038
Net effect of dilutive stock options, restricted stock units and restricted stock awards	2,932,325		3,069,885		2,961,810	3,115,948
Weighted average common shares for diluted earnings per share	57,614,284		56,587,009		57,426,563	56,414,986
Net income per share:
Basic (in dollars per share)	$ 1.07		$ 0.94		$ 2.19	$ 2.15
Diluted (in dollars per share)	$ 1.02		$ 0.89		$ 2.08	$ 2.03
Anti-dilutive options not included in the calculation (in shares)	168,451		155,142		97,327	104,186