BUSINESS SEGMENT RESULTS (Schedule of Business Segment Results) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Investment securities	$ 2,123,778		$ 2,123,778		$ 2,351,931
Total loans	2,952,119		2,952,119		2,857,095
FRB and FHLB stock	30,388		30,388		27,357
Total assets	5,882,354		5,882,354		5,918,983
Deposits	4,806,034		4,806,034		4,813,895
Securities sold under agreements to repurchase	57,572		57,572		43,143
Subordinated debentures	354,248		354,248		354,210
Stockholders' equity	506,228	270,799	506,228	270,799	488,256	299,959
Interest income	42,587	43,732	84,776	87,718
Interest expense	5,063	5,975	10,912	12,124
Net interest income (loss)	37,524	37,757	73,864	75,594
Provision for loan losses	0	0	0	0
Net interest income (loss) after provision for loan losses	37,524	37,757	73,864	75,594
Noninterest income	14,214	18,943	28,889	34,338
Noninterest expense	43,588	44,143	86,336	88,190
Income (loss) from continuing operations before provision (benefit) for income taxes	8,150	12,557	16,417	21,742
Provision (benefit) for income taxes	2,918	(345)	5,835	20
Net income (loss) from continuing operations, net of tax	5,232	12,902	10,582	21,722
Loss from discontinued operations, net of tax	0	(3,334)	0	(5,398)
Net income (loss)	5,232	9,568	10,582	16,324
Net (loss) income attributable to noncontrolling interest in subsidiary	1	105	(54)	151
Net income (loss) attributable to First Banks, Inc.	5,231	9,463	10,636	16,173
First Bank [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Investment securities	2,123,778		2,123,778		2,351,931
Total loans	2,952,119		2,952,119		2,857,095
FRB and FHLB stock	30,388		30,388		27,357
Total assets	5,830,155		5,830,155		5,865,160
Deposits	4,816,077		4,816,077		4,815,792
Securities sold under agreements to repurchase	57,572		57,572		43,143
Subordinated debentures	0		0		0
Stockholders' equity	880,667		880,667		931,561
Interest income	42,557	43,732	84,746	87,718
Interest expense	2,041	2,244	4,092	4,717
Net interest income (loss)	40,516	41,488	80,654	83,001
Provision for loan losses	0	0	0	0
Net interest income (loss) after provision for loan losses	40,516	41,488	80,654	83,001
Noninterest income	14,124	18,831	28,683	34,115
Noninterest expense	43,607	44,025	86,600	87,888
Income (loss) from continuing operations before provision (benefit) for income taxes	11,033	16,294	22,737	29,228
Provision (benefit) for income taxes	1,901	(128)	6,021	20
Net income (loss) from continuing operations, net of tax	9,132	16,422	16,716	29,208
Loss from discontinued operations, net of tax	0	(3,334)	0	(5,398)
Net income (loss)	9,132	13,088	16,716	23,810
Net (loss) income attributable to noncontrolling interest in subsidiary	1	105	(54)	151
Net income (loss) attributable to First Banks, Inc.	9,131	12,983	16,770	23,659
Corporate, Other and Intercompany Reclassifications [Member]
Segment Reporting Information [Line Items]
Investment securities	0		0		0
Total loans	0		0		0
FRB and FHLB stock	0		0		0
Total assets	52,199		52,199		53,823
Deposits	(10,043)		(10,043)		(1,897)
Securities sold under agreements to repurchase	0		0		0
Subordinated debentures	354,248		354,248		354,210
Stockholders' equity	(374,439)		(374,439)		(443,305)
Interest income	30	0	30	0
Interest expense	3,022	3,731	6,820	7,407
Net interest income (loss)	(2,992)	(3,731)	(6,790)	(7,407)
Provision for loan losses	0	0	0	0
Net interest income (loss) after provision for loan losses	(2,992)	(3,731)	(6,790)	(7,407)
Noninterest income	90	112	206	223
Noninterest expense	(19)	118	(264)	302
Income (loss) from continuing operations before provision (benefit) for income taxes	(2,883)	(3,737)	(6,320)	(7,486)
Provision (benefit) for income taxes	1,017	(217)	(186)	0
Net income (loss) from continuing operations, net of tax	(3,900)	(3,520)	(6,134)	(7,486)
Loss from discontinued operations, net of tax	0	0	0	0
Net income (loss)	(3,900)	(3,520)	(6,134)	(7,486)
Net (loss) income attributable to noncontrolling interest in subsidiary	0	0	0	0
Net income (loss) attributable to First Banks, Inc.	$ (3,900)	$ (3,520)	$ (6,134)	$ (7,486)