Condensed Statements of Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Other income									$ 429	$ 411	$ 2,459
Income tax expense	(2,931)	(3,609)	(3,223)	(2,561)	(2,436)	(2,539)	(2,537)	(3,396)	(12,324)	(10,908)	(14,128)
Net income	5,715	7,043	7,007	5,725	5,324	5,412	5,435	7,141	25,490	23,312	28,577
Dividends on preferred stock	227	228	227	228	252	261	253	258	910	1,024	1,058
Net income available to common shareholders	5,488	6,815	6,780	5,497	5,072	5,151	5,182	6,883	24,580	22,288	27,519
First Community Bancshares, Inc.
Condensed Financial Statements, Captions [Line Items]
Cash dividends received from subsidiary bank									14,148	43,900	8,105
Other income									515	726	445
Operating expense									(1,793)	(1,647)	(1,318)
Income tax expense									511	368	(55)
Equity in undistributed earnings of subsidiary									12,109	(20,035)	21,400
Net income									25,490	23,312	28,577
Dividends on preferred stock									910	1,024	1,058
Net income available to common shareholders									$ 24,580	$ 22,288	$ 27,519