NONINTEREST INCOME - Investment Management and Fiduciary Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Trust fees
Revenue from External Customer [Line Items]
Noninterest fee income	$ 9,303	$ 6,632	$ 23,565	$ 19,884
Wealth management and advisory fees
Revenue from External Customer [Line Items]
Noninterest fee income	3,963	3,827	11,592	11,104
Investment management and fiduciary income
Revenue from External Customer [Line Items]
Noninterest fee income	$ 13,266	$ 10,459	$ 35,157	$ 30,988