Loan Servicing (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Banking and Thrift [Abstract]
Unpaid Principal Balance Of Loans Serviced For Others	$ 167,879	$ 136,867	$ 163,139

Unpaid Principal Balance Of Loans Serviced For Others

No definition available.

Name:	frme_UnpaidPrincipalBalanceOfLoansServicedForOthers
Namespace Prefix:	frme_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant