REGULATORY CAPITAL AND OTHER REGULATORY MATTERS (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
First Banks Inc [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital	$ 98,418	$ 93,542
Total Capital to Risk-Weighted Assets	2.72%	2.57%
Total Capital Required for Capital Adequacy	8.00%
Tier One Capital	49,209	46,771
Tier One Capital to Risk-Weighted Assets	1.36%	1.28%
Tier One Capital Required for Capital Adequacy	4.00%
Tier One Leverage Capital	49,209	46,771
Tier One Leverage Capital to Average Assets	0.79%	0.73%
Tier One Leverage Capital Required for Capital Adequacy	4.00%
First Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital	636,522	626,177
Total Capital to Risk-Weighted Assets	17.60%	17.18%
Total Capital Required for Capital Adequacy	8.00%
Total Capital Required to be Well Capitalized	10.00%
Tier One Capital	590,748	580,026
Tier One Capital to Risk-Weighted Assets	16.33%	15.92%
Tier One Capital Required for Capital Adequacy	4.00%
Tier One Capital Required to be Well Capitalized	6.00%
Tier One Leverage Capital	$ 590,748	$ 580,026
Tier One Leverage Capital to Average Assets	9.50%	9.13%
Tier One Leverage Capital Required for Capital Adequacy	4.00%
Tier One Leverage Capital Required to be Well Capitalized	5.00%

The amount of total capital as defined in the regulations.

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The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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Total Capital divided by risk weighted assets as defined in the regulations.

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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

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Tier 1 Risk Based Capital as defined in the regulations.

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The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

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Tier 1 capital divided by risk weighted assets as defined by regulations.

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