BUSINESS COMBINATIONS - Schedule of Pro Forma Information (Details) - Hamilton, Atlantic, And USPF $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Business Acquisition [Line Items]
Net interest income and noninterest income	$ 95,265
Net income	26,876
Net income available to common shareholders	$ 26,876
Income per common share available to common shareholders – basic (in dollars per share) | $ / shares	$ 0.70
Income per common share available to common shareholders – diluted (in dollars per share) | $ / shares	$ 0.70
Average number of shares outstanding, basic (in shares) | shares	38,246
Average number of shares outstanding, diluted (in shares) | shares	38,529