BUSINESS COMBINATIONS - Schedule of Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Business Combinations [Abstract]
Net interest income and noninterest income	$ 284,774	$ 200,132	$ 357,890	$ 392,386
Net income	32,943	44,495	52,693	92,348
Net income available to common shareholders	$ 32,943	$ 44,495	$ 52,693	$ 92,348
Income per common share available to common shareholders – basic (in dollars per share)	$ 0.48	$ 0.64	$ 0.76	$ 1.33
Income per common share available to common shareholders – diluted (in dollars per share)	$ 0.48	$ 0.64	$ 0.76	$ 1.33
Average number of shares outstanding, basic (in shares)	69,192	69,492	69,235	69,535
Average number of shares outstanding, diluted (in shares)	69,293	69,519	69,413	69,576