Quarterly report pursuant to Section 13 or 15(d)

COMMITMENTS AND CONTINGENT LIABILITIES - Narrative (Details)

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COMMITMENTS AND CONTINGENT LIABILITIES - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2017
Dec. 31, 2016
Sep. 28, 2015
Loss Contingencies [Line Items]        
Maturity period of majority of standby letters of credit   P2Y    
Maturity period of Commercial letters of credit   P90D    
Maturity period of forward contracts relating mortgage banking business   1 year    
Cyberco Litigation        
Loss Contingencies [Line Items]        
Bankruptcy Court recommended judgment amount in Cyberco case, principal       $ 72,000
Standby Letters of Credit        
Loss Contingencies [Line Items]        
Carrying amount of deferred revenue associated with guarantees $ 5,000 $ 5,000 $ 8,000  
Outstanding standby letters of credit 547,689 547,689 637,182  
Commitments to Sell Loans        
Loss Contingencies [Line Items]        
Commitments to sell residential real estate loans 1,000,000 1,000,000 $ 819,000  
Maximum        
Loss Contingencies [Line Items]        
Aggregate range of reasonably possible losses current legal proceedings 65,000 $ 65,000    
Cash [Member] | FirstMerit Overdraft Litigation [Member]        
Loss Contingencies [Line Items]        
Settlement amount 9,000      
Debt forgiveness [Member] | FirstMerit Overdraft Litigation [Member]        
Loss Contingencies [Line Items]        
Settlement amount 7,000      
Insurance Settlement [Member] | FirstMerit Overdraft Litigation [Member]        
Loss Contingencies [Line Items]        
Settlement amount $ 4,400      
Reimbursement percent 49.00%