Note 22 - Fair Value (Detail) - Collateralized Residential Mortgage Obligations	Dec. 31, 2011
Weighted-average coupon rate	4.50%
Weighted-average coupon rate	1.80%
Weighted-average maturity, in years	2.2
Weighted-average maturity, in years	3.9
Information on underlying residential mortgages:
Origination dates	2000 to 2010
Origination dates	2000 to 2010
Weighted-average coupon rate	5.70%
Weighted-average coupon rate	5.80%
Weighted-average maturity, in years	8.3
Weighted-average maturity, in years	9.2

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- Definition

This item represents origination dates on collateralized mortgage obligations.

+ References

No definition available.

+ Details

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- Definition

This item represents origination dates on other mortgage backed obligations.

+ References

No definition available.

+ Details

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- Definition

This item represents the weighted average coupon rate on collateralized mortgage obligations.

+ References

No definition available.

+ Details

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- Definition

This item represents the weighted average coupon rate on other mortgage backed securities.

+ References

No definition available.

+ Details

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Namespace Prefix:	fmbi_
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- Definition

This item represents the weighted average coupon rate underlying collateralized mortgage obligations.

+ References

No definition available.

+ Details

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Namespace Prefix:	fmbi_
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- Definition

This item represents the weighted average coupon rate underlying mortgage backed securities.

+ References

No definition available.

+ Details

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- Definition

This item represents the weighted average maturity in years on collateralized mortgage obligations.

+ References

No definition available.

+ Details

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- Definition

This item represents the weighted average maturity in years on other mortgage backed securities.

+ References

No definition available.

+ Details

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- Definition

This item represents the weighted average maturity in years on underlying collateralized mortgage obligations.

+ References

No definition available.

+ Details

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Namespace Prefix:	fmbi_
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- Definition

This item represents the weighted average maturity in years on underlying other mortgage backed securities.

+ References

No definition available.

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