Allowance for Loan Losses - Summary of Average Recorded Investment and Interest Income Recognized for TDRs (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Financing Receivable Modifications [Line Items]
Total loans Average Recorded Investment	$ 4,531	$ 4,568
Total loans Interest Income Recognized	20	48
Construction And Land Development
Financing Receivable Modifications [Line Items]
Total loans Average Recorded Investment	1,902	1,471
Total loans Interest Income Recognized	4	8
1-4 Family residential [Member]
Financing Receivable Modifications [Line Items]
Total loans Average Recorded Investment	1,292	1,463
Total loans Interest Income Recognized	14	18
Commercial and industrial [Member]
Financing Receivable Modifications [Line Items]
Total loans Average Recorded Investment	194	172
Total loans Interest Income Recognized	1
Consumer Portfolio Segment
Financing Receivable Modifications [Line Items]
Total loans Average Recorded Investment	378	217
Total loans Interest Income Recognized	1
Troubled Debt Restructurings [Member]
Financing Receivable Modifications [Line Items]
Total loans Average Recorded Investment	1,511	821
Total loans Interest Income Recognized	16	15
Troubled Debt Restructurings [Member] | Construction And Land Development
Financing Receivable Modifications [Line Items]
Total loans Average Recorded Investment	209	459
Total loans Interest Income Recognized	4	7
Troubled Debt Restructurings [Member] | 1-4 Family residential [Member]
Financing Receivable Modifications [Line Items]
Total loans Average Recorded Investment	1,257	359
Total loans Interest Income Recognized	11	8
Troubled Debt Restructurings [Member] | Commercial and industrial [Member]
Financing Receivable Modifications [Line Items]
Total loans Average Recorded Investment	1	3
Troubled Debt Restructurings [Member] | Consumer Portfolio Segment
Financing Receivable Modifications [Line Items]
Total loans Average Recorded Investment	44
Total loans Interest Income Recognized	$ 1