BUSINESS COMBINATIONS - Schedule of Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Business Combinations [Abstract]
Net interest income and noninterest income	$ 225,762	$ 201,618	$ 618,148	$ 602,620
Net income	73,213	54,481	165,603	140,952
Net income available to common shareholders	$ 73,213	$ 54,481	$ 165,603	$ 140,952
Income per common share available to common shareholders – basic (in dollars per share)	$ 1.06	$ 0.78	$ 2.38	$ 2.02
Income per common share available to common shareholders – diluted (in dollars per share)	$ 1.05	$ 0.78	$ 2.38	$ 2.02
Average number of shares outstanding, basic (in shares)	69,372	69,696	69,469	69,628
Average number of shares outstanding, diluted (in shares)	69,600	69,867	69,590	69,800