Note 20 - Commitments, Guarantees, and Contingent Liabilities (Detail) - Repurchases and Charge-Offs of Recourse Loans (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2010	Dec. 31, 2009
Recourse loans repurchased during the year	$ 241	$ 767
Recourse loans charged-off during the year	$ 174	$ 73

This element represents the recorded value of non-performing loans the Company was obligated to repurchase during the year, in accordance with a securitization agreement.

No definition available.

Name:	fmbi_RecourseLoansRepurchasedDuringTheYear
Namespace Prefix:	fmbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration