INVESTMENT SECURITIES - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) position	Mar. 31, 2018 USD ($)
Investments, Debt and Equity Securities [Abstract]
Percentage of debt securities considered to be of investment-grade	97.00%
Maximum percentage of any general obligation bonds in one state	12.00%
Securities in unrealized loss positions, number of positions	690
Securities, number of positions	1,430
Other-than-temporary impairments | $	$ 0.0	$ 0.0