OTHER COMPREHENSIVE INCOME - RECLASSIFICATION (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Significant amounts reclassified out of each component of AOCI
Interest expense on deposits	$ (3,360)	$ (1,879)
Interest expense on FHLB advances	(2,274)	(2,292)
Total interest expense	(6,168)	(4,445)
Income tax expense	(7,441)	(10,054)
NET INCOME	27,469	20,017
Unrealized gain (loss) on cash flow hedge | Reclassification out of Accumulated Other Comprehensive Income
Significant amounts reclassified out of each component of AOCI
Interest expense on deposits	(14)	(34)
Interest expense on FHLB advances	(12)	(32)
Total interest expense	(26)	(66)
Income tax expense	9	23
NET INCOME	$ (17)	$ (43)