BUSINESS COMBINATIONS - Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Combinations [Abstract]
Net interest income and noninterest income	$ 828,612	$ 803,281	$ 747,700
Net income	228,798	196,352	138,359
Net income available to common shareholders	$ 228,798	$ 196,352	$ 138,359
Income per common share available to common shareholders – basic (in dollars per share)	$ 3.29	$ 2.82	$ 2.00
Income per common share available to common shareholders – diluted (in dollars per share)	$ 3.29	$ 2.82	$ 1.99
Average number of shares outstanding, basic (in shares)	69,462,000	69,642,000	69,140,000
Average number of shares outstanding, diluted (in shares)	69,614,000	69,748,000	69,456,000