BUSINESS SEGMENT RESULTS (Schedule of Business Segment Results) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Balance sheet information:
Investment securities	$ 2,675,280	$ 2,470,704	$ 1,483,659
Loans, net of net deferred loan fees	2,930,747	3,284,279	4,492,284
FRB and FHLB stock	27,329	27,078	30,121
Goodwill and other intangible assets	125,267	125,267	129,054
Assets held for sale	0	0	2,266
Assets of discontinued operations	6,706	6,913	43,532
Total assets	6,509,126	6,608,913	7,378,128
Deposits	5,492,847	5,623,055	6,458,415
Other borrowings	26,025	51,170	31,761
Subordinated debentures	354,133	354,057	353,981
Liabilities held for sale	0	0	23,406
Liabilities of discontinued operations	155,711	174,737	94,184
Stockholders’ equity	299,959	263,671	307,295	522,380
Income statement information:
Interest income	202,565	233,296	312,468
Interest expense	30,088	44,539	76,020
Net interest income	172,477	188,757	236,448
Provision for loan losses	2,000	69,000	214,000
Net interest income after provision for loan losses	170,477	119,757	22,448
Noninterest income	66,206	62,194	78,492
Amortization of intangible assets	0	3,024	3,292
Other noninterest expense	205,318	227,222	295,347
Income (loss) from continuing operations before provision (benefit) for income taxes	31,365	(48,295)	(197,699)
Provision (benefit) for income taxes	(139)	(10,654)	4,114
Net income (loss) from continuing operations	31,504	(37,641)	(201,813)
(Loss) income from discontinued operations, net of tax	(5,523)	(6,459)	3,562
Net income (loss)	25,981	(44,100)	(198,251)
Net loss attributable to noncontrolling interest in subsidiary	(297)	(2,950)	(6,514)
Net income (loss) attributable to First Banks, Inc.	26,278	(41,150)	(191,737)
Corporate, Other and Intercompany Reclassifications
Balance sheet information:
Investment securities	0	0	0
Loans, net of net deferred loan fees	0	0	0
FRB and FHLB stock	0	0	0
Goodwill and other intangible assets	0	0	0
Assets held for sale	0	0	0
Assets of discontinued operations	0	0	0
Total assets	13,900	15,398	16,422
Deposits	(2,777)	(2,834)	(3,653)
Other borrowings	0	0	0
Subordinated debentures	354,133	354,057	353,981
Liabilities held for sale	0	0	0
Liabilities of discontinued operations	0	0	0
Stockholders’ equity	(451,293)	(416,954)	(386,163)
Income statement information:
Interest income	121	85	135
Interest expense	14,838	13,612	12,993
Net interest income	(14,717)	(13,527)	(12,858)
Provision for loan losses	0	0	0
Net interest income after provision for loan losses	(14,717)	(13,527)	(12,858)
Noninterest income	405	219	39
Amortization of intangible assets	0	0	0
Other noninterest expense	1,510	(378)	639
Income (loss) from continuing operations before provision (benefit) for income taxes	(15,822)	(12,930)	(13,458)
Provision (benefit) for income taxes	(369)	(46)	(172)
Net income (loss) from continuing operations	(15,453)	(12,884)	(13,286)
(Loss) income from discontinued operations, net of tax	0	0	0
Net income (loss)	(15,453)	(12,884)	(13,286)
Net loss attributable to noncontrolling interest in subsidiary	0	0	0
Net income (loss) attributable to First Banks, Inc.	(15,453)	(12,884)	(13,286)
First Bank
Balance sheet information:
Investment securities	2,675,280	2,470,704	1,483,659
Loans, net of net deferred loan fees	2,930,747	3,284,279	4,492,284
FRB and FHLB stock	27,329	27,078	30,121
Goodwill and other intangible assets	125,267	125,267	129,054
Assets held for sale	0	0	2,266
Assets of discontinued operations	6,706	6,913	43,532
Total assets	6,495,226	6,593,515	7,361,706
Deposits	5,495,624	5,625,889	6,462,068
Other borrowings	26,025	51,170	31,761
Subordinated debentures	0	0	0
Liabilities held for sale	0	0	23,406
Liabilities of discontinued operations	155,711	174,737	94,184
Stockholders’ equity	751,252	680,625	693,458
Income statement information:
Interest income	202,444	233,211	312,333
Interest expense	15,250	30,927	63,027
Net interest income	187,194	202,284	249,306
Provision for loan losses	2,000	69,000	214,000
Net interest income after provision for loan losses	185,194	133,284	35,306
Noninterest income	65,801	61,975	78,453
Amortization of intangible assets	0	3,024	3,292
Other noninterest expense	203,808	227,600	294,708
Income (loss) from continuing operations before provision (benefit) for income taxes	47,187	(35,365)	(184,241)
Provision (benefit) for income taxes	230	(10,608)	4,286
Net income (loss) from continuing operations	46,957	(24,757)	(188,527)
(Loss) income from discontinued operations, net of tax	(5,523)	(6,459)	3,562
Net income (loss)	41,434	(31,216)	(184,965)
Net loss attributable to noncontrolling interest in subsidiary	(297)	(2,950)	(6,514)
Net income (loss) attributable to First Banks, Inc.	$ 41,731	$ (28,266)	$ (178,451)