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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Business Combinations [Abstract]
Net interest income and noninterest income	$ 321,556	$ 225,762	$ 808,654	$ 618,148
Net income	116,111	73,213	168,804	165,561
Net income available to common shareholders	$ 116,111	$ 73,213	$ 168,804	$ 165,561
Income per common share available to common shareholders – basic (in dollars per share)	$ 1.68	$ 1.06	$ 2.44	$ 2.38
Income per common share available to common shareholders – diluted (in dollars per share)	$ 1.67	$ 1.05	$ 2.43	$ 2.38
Average number of shares outstanding, basic (in shares)	69,231	69,372	69,243	69,469
Average number of shares outstanding, diluted (in shares)	69,346	69,600	69,403	69,590