ASSETS ACQUIRED IN FDIC-ASSISTED ACQUISITIONS - Narrative (Details) $ in Thousands	3 Months Ended					9 Months Ended	12 Months Ended	34 Months Ended
	Mar. 31, 2017	Sep. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2017 USD ($)	Dec. 31, 2012 USD ($)	Jul. 31, 2012 acquisition	Dec. 31, 2016 USD ($)
Business Combinations [Abstract]
Number of FDIC-assisted acquisitions | acquisition								10
FDIC loss-sharing payable						$ 8,200
Clawback liability						9,600			$ 9,300
Current activity incurred						419
Remaining indemnification						$ 1,000
Single Family Residential Assets (SFR)
Business Combinations [Abstract]
Coverage period for acquisitions						10 years
Single Family Residential Assets (SFR) | American United Bank [Member]
Business Combinations [Abstract]
Reimbursement revenue							$ 87
Non-Single Family Assets (NSF)
Business Combinations [Abstract]
Coverage period for acquisitions						8 years
Coverage period for acquisitions, losses and recoveries both covered						5 years
Coverage period for acquisitions, only recoveries, net of expenses covered						3 years
Non-Single Family Assets (NSF) | AUB and USB
Business Combinations [Abstract]
Anniversary mark for acquisition agreements					5 years
Non-Single Family Assets (NSF) | Satilla Community Bank (“SCB”)
Business Combinations [Abstract]
Anniversary mark for acquisition agreements				5 years
Non-Single Family Assets (NSF) | FBJ, TBC, and DBT
Business Combinations [Abstract]
Anniversary mark for acquisition agreements			5 years
Non-Single Family Assets (NSF) | HTB and OGB
Business Combinations [Abstract]
Anniversary mark for acquisition agreements		5 years
Non-Single Family Assets (NSF) | Central Bank of Georgia (“CBG”)
Business Combinations [Abstract]
Anniversary mark for acquisition agreements	5 years