LOANS - Rollforward of Purchased Loans (Details) - Purchased Loans - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 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	(1,060)	(1,860)
Additions due to acquisitions	2,056,918	0
Accretion	4,340	6,165
Transfers to purchased other real estate owned	(556)	(3,281)
Payments received	(108,727)	(119,716)
Ending balance	$ 2,812,510	$ 950,499