REGULATORY CAPITAL AND OTHER REGULATORY MATTERS (Schedule of Regulatory Capital ) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
First Banks, Inc. (Consolidated) [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital, Amount	$ 608,834	$ 475,312
Total Capital to Risk-Weighted Assets, Ratio	15.27%	12.25%
Total Capital Required for Capital Adequacy, Ratio	8.00%	8.00%
Tier One Capital, Amount	$ 311,829	$ 284,396
Tier One Capital to Risk-Weighted Assets, Ratio	7.82%	7.33%
Tier One Capital Required for Capital Adequacy, Ratio	6.00%	4.00%
Common Equity Tier One Risk Based Capital, Amount	$ (25,346)
Common Equity Tier One Capital To Risk-Weighted Assets, Ratio	(0.64%)
Common Equity Tier One Capital Required For Capital Adequacy, Ratio	4.50%
Tier One Leverage Capital, Amount	$ 311,829	$ 284,396
Tier One Leverage Capital to Average Assets, Ratio	5.31%	5.01%
Tier One Leverage Capital Required for Capital Adequacy, Ratio	4.00%	4.00%
First Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital, Amount	$ 682,301	$ 691,350
Total Capital to Risk-Weighted Assets, Ratio	17.01%	17.81%
Total Capital Required for Capital Adequacy, Ratio	8.00%	8.00%
Total Capital Required to be Well Capitalized, Ratio	10.00%	10.00%
Tier One Capital, Amount	$ 630,575	$ 642,593
Tier One Capital to Risk-Weighted Assets, Ratio	15.72%	16.55%
Tier One Capital Required for Capital Adequacy, Ratio	6.00%	4.00%
Tier One Capital Required to be Well Capitalized, Ratio	8.00%	6.00%
Common Equity Tier One Risk Based Capital, Amount	$ 630,575
Common Equity Tier One Capital To Risk-Weighted Assets, Ratio	15.72%
Common Equity Tier One Capital Required For Capital Adequacy, Ratio	4.50%
Common Equity Tier One Capital To Be Well Capitalized, Ratio	6.50%
Tier One Leverage Capital, Amount	$ 630,575	$ 642,593
Tier One Leverage Capital to Average Assets, Ratio	10.69%	11.35%
Tier One Leverage Capital Required for Capital Adequacy, Ratio	4.00%	4.00%
Tier One Leverage Capital Required to be Well Capitalized, Ratio	5.00%	5.00%