BUSINESS COMBINATIONS - Schedule of Pro Forma Information (Details) - Hamilton, Atlantic, And USPF - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Business Acquisition [Line Items]
Net interest income and noninterest income	$ 132,540	$ 119,137	$ 255,652	$ 233,949
Net income	14,603	30,913	49,506	59,643
Net income available to common shareholders	$ 14,603	$ 30,913	$ 49,506	$ 59,643
Income per common share available to common shareholders – basic (in dollars per share)	$ 0.31	$ 0.65	$ 1.04	$ 1.28
Income per common share available to common shareholders – diluted (in dollars per share)	$ 0.31	$ 0.65	$ 1.04	$ 1.27
Average number of shares outstanding, basic (in shares)	47,398	47,287	47,412	46,554
Average number of shares outstanding, diluted (in shares)	47,676	47,614	47,689	46,881