EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator for basic and diluted earnings per share:
Net income	$ 67,002	$ 58,777	$ 60,754	$ 65,618	$ 50,255	$ 64,418	$ 186,533	$ 180,291
Numerator for basic and diluted earnings per share	$ 67,002			$ 65,618			$ 186,533	$ 180,291
Denominator:
Weighted average common shares for basic earnings per share	54,877,666			53,851,865			54,603,903	53,485,339
Net effect of dilutive stock options, restricted stock units and restricted stock awards	2,966,689			3,111,002			2,963,436	3,114,299
Weighted average common shares for diluted earnings per share	57,844,355			56,962,867			57,567,339	56,599,638
Net income per share:
Basic (in dollars per share)	$ 1.22			$ 1.22			$ 3.42	$ 3.37
Diluted (in dollars per share)	$ 1.16			$ 1.15			$ 3.24	$ 3.19
Anti-dilutive options not included in the calculation (in shares)	143,617			157,316			112,757	121,896