BUSINESS COMBINATION - Schedule of Pro Forma Information (Details) - US Premium Financing Holding Company - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Business Acquisition [Line Items]
Net interest income and noninterest income	$ 95,265	$ 86,296
Net income	26,876	22,174
Net income available to common shareholders	$ 26,876	$ 22,174
Income per common share available to common shareholders – basic (in dollars per share)	$ 0.70	$ 0.61
Income per common share available to common shareholders – diluted (in dollars per share)	$ 0.70	$ 0.60
Average number of shares outstanding, basic (in shares)	38,246	36,633
Average number of shares outstanding, diluted (in shares)	38,529	37,009