Loans and Allowance for Loan Losses - Troubled Debt Restructuring Categorized by Loan (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014 Contract	Dec. 31, 2013 Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts	4	12
Pre Modification Outstanding Recorded Investment	$ 624	$ 6,641
Post Modification Outstanding Recorded Investment, Net of Related Allowance	624	4,410
Residential 1-4 Family [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	3	6
Pre Modification Outstanding Recorded Investment	602	800
Post Modification Outstanding Recorded Investment, Net of Related Allowance	602	800
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts
Pre Modification Outstanding Recorded Investment
Post Modification Outstanding Recorded Investment, Net of Related Allowance
Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts		1
Pre Modification Outstanding Recorded Investment		282
Post Modification Outstanding Recorded Investment, Net of Related Allowance		282
Farmland [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts
Pre Modification Outstanding Recorded Investment
Post Modification Outstanding Recorded Investment, Net of Related Allowance
Equity Lines of Credit [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts
Pre Modification Outstanding Recorded Investment
Post Modification Outstanding Recorded Investment, Net of Related Allowance
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts
Pre Modification Outstanding Recorded Investment
Post Modification Outstanding Recorded Investment, Net of Related Allowance
Agricultural Installment and Other [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts		2
Pre Modification Outstanding Recorded Investment		13
Post Modification Outstanding Recorded Investment, Net of Related Allowance		13
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	1	2
Pre Modification Outstanding Recorded Investment	22	5,522
Post Modification Outstanding Recorded Investment, Net of Related Allowance	22	3,291
Second Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts		1
Pre Modification Outstanding Recorded Investment		24
Post Modification Outstanding Recorded Investment, Net of Related Allowance		$ 24