LOANS - Rollforward of Purchased Loans (Details) - Purchased Loans - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 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	(1,314)	(1,761)
Additions due to acquisitions	2,054,440	0
Accretion	8,083	9,023
Transfers to purchased other real estate owned	(2,434)	(4,294)
Payments received	(208,910)	(155,033)
Ending balance	$ 2,711,460	$ 917,126