Quarterly report pursuant to Section 13 or 15(d)

LOANS / LEASES AND ALLOWANCE FOR CREDIT LOSSES LOANS / LEASES AND ALLOWANCE FOR CREDIT LOSSES - Certain Loans Acquired Ending and Unpaid Balances (Details)

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LOANS / LEASES AND ALLOWANCE FOR CREDIT LOSSES LOANS / LEASES AND ALLOWANCE FOR CREDIT LOSSES - Certain Loans Acquired Ending and Unpaid Balances (Details) - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Purchased Credit Impaired, Ending Balance $ 90,111 $ 102,380
Commercial | Commercial and Industrial    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Purchased Credit Impaired, Ending Balance 67,514 68,338
Commercial | Commercial Real Estate    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Purchased Credit Impaired, Ending Balance 22,597 34,042
FirstMerit Corporation    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Purchased Credit Impaired, Ending Balance 90,111 102,380
Purchased Credit Impaired, Unpaid Balance 135,991 156,351
FirstMerit Corporation | Commercial | Commercial and Industrial    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Purchased Credit Impaired, Ending Balance 67,514 68,338
Purchased Credit Impaired, Unpaid Balance 97,946 100,031
FirstMerit Corporation | Commercial | Commercial Real Estate    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Purchased Credit Impaired, Ending Balance 22,597 34,042
Purchased Credit Impaired, Unpaid Balance $ 38,045 $ 56,320