BUSINESS SEGMENT RESULTS (Schedule of Business Segment Results) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Balance sheet information:
Investment securities	$ 2,063,837	$ 2,351,931	$ 2,675,280
Total loans	3,149,243	2,857,095	2,930,747
FRB and FHLB stock	30,458	27,357	27,329
Goodwill	0	0	125,267
Assets of discontinued operations	0	0	6,706
Total assets	5,935,519	5,918,983	6,509,126
Deposits	4,849,504	4,813,895	5,492,847
Securities sold under agreements to repurchase	64,875	43,143	26,025
Subordinated debentures	354,286	354,210	354,133
Liabilities of discontinued operations	0	0	155,711
Stockholders’ equity	512,444	488,256	299,959	263,671
Income statement information:
Interest income	168,728	172,810	200,803
Interest expense	21,178	24,104	29,611
Net interest income (loss)	147,550	148,706	171,192
(Benefit) provision for loan losses	(7,000)	(5,000)	2,000
Net interest income (loss) after (benefit) provision for loan losses	154,550	153,706	169,192
Noninterest income	56,040	63,977	64,635
Goodwill impairment	0	107,267	0
Other noninterest expense (excluding goodwill impairment)	176,852	178,217	199,164
Income (loss) from continuing operations, before provision (benefit) for income taxes	33,738	(67,801)	34,663
Provision (benefit) for income taxes	12,159	(288,501)	(139)
Net income (loss) from continuing operations, net of tax	21,579	220,700	34,802
Income (loss) from discontinued operations, net of tax	0	21,223	(8,821)
Net income (loss)	21,579	241,923	25,981
Net (loss) income attributable to noncontrolling interest in subsidiary	(76)	179	(297)
Net income (loss) attributable to First Banks, Inc.	21,655	241,744	26,278
First Bank [Member] | Operating Segments [Member]
Balance sheet information:
Investment securities	2,063,837	2,351,931	2,675,280
Total loans	3,149,243	2,857,095	2,930,747
FRB and FHLB stock	30,458	27,357	27,329
Goodwill	0	0	125,267
Assets of discontinued operations	0	0	6,706
Total assets	5,882,222	5,865,160	6,495,226
Deposits	4,871,140	4,815,792	5,495,624
Securities sold under agreements to repurchase	64,875	43,143	26,025
Subordinated debentures	0	0	0
Liabilities of discontinued operations	0	0	155,711
Stockholders’ equity	871,301	931,561	751,252
Income statement information:
Interest income	168,653	172,810	200,682
Interest expense	8,276	9,054	14,773
Net interest income (loss)	160,377	163,756	185,909
(Benefit) provision for loan losses	(7,000)	(5,000)	2,000
Net interest income (loss) after (benefit) provision for loan losses	167,377	168,756	183,909
Noninterest income	55,650	63,523	64,230
Goodwill impairment	0	107,267	0
Other noninterest expense (excluding goodwill impairment)	176,171	177,307	197,654
Income (loss) from continuing operations, before provision (benefit) for income taxes	46,856	(52,295)	50,485
Provision (benefit) for income taxes	14,724	(249,137)	230
Net income (loss) from continuing operations, net of tax	32,132	196,842	50,255
Income (loss) from discontinued operations, net of tax	0	21,223	(8,821)
Net income (loss)	32,132	218,065	41,434
Net (loss) income attributable to noncontrolling interest in subsidiary	(76)	179	(297)
Net income (loss) attributable to First Banks, Inc.	32,208	217,886	41,731
Corporate, Other and Intercompany Reclassifications [Member]
Balance sheet information:
Investment securities	0	0	0
Total loans	0	0	0
FRB and FHLB stock	0	0	0
Goodwill	0	0	0
Assets of discontinued operations	0	0	0
Total assets	53,297	53,823	13,900
Deposits	(21,636)	(1,897)	(2,777)
Securities sold under agreements to repurchase	0	0	0
Subordinated debentures	354,286	354,210	354,133
Liabilities of discontinued operations	0	0	0
Stockholders’ equity	(358,857)	(443,305)	(451,293)
Income statement information:
Interest income	75	0	121
Interest expense	12,902	15,050	14,838
Net interest income (loss)	(12,827)	(15,050)	(14,717)
(Benefit) provision for loan losses	0	0	0
Net interest income (loss) after (benefit) provision for loan losses	(12,827)	(15,050)	(14,717)
Noninterest income	390	454	405
Goodwill impairment	0	0	0
Other noninterest expense (excluding goodwill impairment)	681	910	1,510
Income (loss) from continuing operations, before provision (benefit) for income taxes	(13,118)	(15,506)	(15,822)
Provision (benefit) for income taxes	(2,565)	(39,364)	(369)
Net income (loss) from continuing operations, net of tax	(10,553)	23,858	(15,453)
Income (loss) from discontinued operations, net of tax	0	0	0
Net income (loss)	(10,553)	23,858	(15,453)
Net (loss) income attributable to noncontrolling interest in subsidiary	0	0	0
Net income (loss) attributable to First Banks, Inc.	$ (10,553)	$ 23,858	$ (15,453)