LOANS - Acquired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Credit impaired acquired loans:
Outstanding principal balance	$ 18,498	$ 30,694
Recorded investment	15,965	25,188
Discount, net	2,533	5,506
Other acquired loans:
Outstanding principal balance	499,939	775,709
Deferred fees, net	(72)	(174)
Recorded investment	498,029	771,104
Discount, net	1,838	4,431
Total acquired loans:
Outstanding principal balance	518,437	806,403
Deferred fees, net	(72)	(174)
Recorded investment	513,994	796,292
Discount, net	4,371	9,937
Changes in the accretable yield for credit impaired acquired loans
Balance at beginning of period	2,544	966
Reclassifications (to) from nonaccretable discount	(20)	3,233
Accretion	(1,399)	(1,655)
Balance at period end	$ 1,125	$ 2,544