LOANS AND ALLOWANCE FOR LOAN LOSSES - Rollforward for Purchased Loans (Details) - Purchased Loans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance, January 1	$ 1,069,191	$ 909,083
Charge-offs	(3,411)	(3,576)
Additions due to acquisitions	0	401,638
Accretion	(11,308)	(16,637)
Transfers to purchased other real estate owned	(5,023)	(7,229)
Payments received	210,470	247,452
Other	0	90
Ending balance	$ 861,595	$ 1,069,191