LOANS - Rollforward of Purchased Loans (Details) - Purchased Loans - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance, January 1	$ 861,595	$ 1,069,191
Charge-offs, net of recoveries	(151)	(803)
Accretion	1,571	3,097
Transfers to purchased other real estate owned	(457)	(1,489)
Payments received	(43,971)	(63,061)
Ending balance	$ 818,587	$ 1,006,935