FNB United Corp. (Parent Company) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Assets
Other assets	$ 26,062	$ 27,691
Total Assets	2,151,565	2,409,108
Liabilities and shareholders’ equity
Borrowed funds	115,030	115,072
Shareholders’ equity	98,445	129,015	(28,837)	98,359
Total Liabilities and Shareholders' Equity	2,151,565	2,409,108
Condensed Statements of Operations
Noninterest income	21,958	21,970	27,622
Interest expense	16,708	23,576	30,635
Noninterest expense	110,206	125,040	75,679
Loss from continuing operations, before income taxes	(41,017)	(130,877)	(129,162)
Income tax expense/(benefit)	(1,039)	641	1,259
Net loss	(40,005)	(137,314)	(131,827)
Preferred stock gain on retirement, net of accretion, and dividends	0	44,592	(3,294)
Net loss to common shareholders	(40,005)	(92,722)	(135,121)
Cash flows from operating activities
Net loss	(40,005)	(137,314)	(131,827)
Adjustments to reconcile net income to net cash provided by operating activities:
Net cash (used in)/provided by operating activities	(35,961)	53,732	32,189
Cash flows from investing activities
Net cash (used in) provided by investing activities	(63,917)	427,498	164,089
Cash flows from financing activities
Proceeds from issuance of common stock	6,694	289,571	0
Cash dividends paid on preferred stock	0	0	(644)
Net cash (used in)/provided by financing activities	(213,928)	(88,408)	(63,382)
Net (Decrease) Increase in Cash and Cash Equivalents	(313,806)	392,822	132,896
Parent Company [Member]
Assets
Cash	606	2,808	180
Investment in subsidiaries	161,007	188,877
Other assets	81	28
Total Assets	161,694	191,713
Liabilities and shareholders’ equity
Accrued liabilities	6,547	5,996
Borrowed funds	56,702	56,702
Shareholders’ equity	98,445	129,015
Total Liabilities and Shareholders' Equity	161,694	191,713
Condensed Statements of Operations
Noninterest income	34	32	33
Interest expense	(1,157)	(1,072)	(1,521)
Noninterest expense	(970)	(3,351)	(343)
Loss from continuing operations, before income taxes	(2,093)	(4,391)	(1,831)
Income tax expense/(benefit)	(311)	723	0
Loss before equity in undistributed net loss of subsidiaries	(1,782)	(5,114)	(1,831)
Equity in undistributed net loss of subsidiaries	(38,223)	(132,200)	(129,996)
Net loss	(40,005)	(137,314)	(131,827)
Preferred stock gain on retirement, net of accretion, and dividends	0	44,592	(3,294)
Net loss to common shareholders	(40,005)	(92,722)	(135,121)
Cash flows from operating activities
Net loss	(40,005)	(137,314)	(131,827)
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed net loss of subsidiaries	38,223	132,200	129,996
Other, net	503	6,638	(451)
Net cash (used in)/provided by operating activities	(1,279)	1,524	(2,282)
Cash flows from investing activities
Downstream cash investment in subsidiary	(6,709)	(287,711)	(1,000)
Net cash (used in) provided by investing activities	(6,709)	(287,711)	(1,000)
Cash flows from financing activities
Proceeds from issuance of common stock	6,694	289,571	0
Cash dividends paid on preferred stock	0	(756)	(644)
Other	(908)	0	0
Net cash (used in)/provided by financing activities	5,786	288,815	(644)
Net (Decrease) Increase in Cash and Cash Equivalents	(2,202)	2,628	(3,926)
Cash at beginning of period	2,808	180	4,106
Cash at end of period	$ 606	$ 2,808	$ 180