Loans and Allowance for Loan Losses - Company's Impaired Loans (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 10,681	$ 10,576
Unpaid Principal Balance	12,359	13,041
Related Allowance	919	1,631
Average Recorded Investment	11,837	17,660
Interest Income Recognized	213	482
With No Related Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	5,497	3,524
Unpaid Principal Balance	5,490	4,322
Average Recorded Investment	6,320	7,960
Interest Income Recognized	34	212
With Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	5,184	7,052
Unpaid Principal Balance	6,869	8,719
Related Allowance	919	1,631
Average Recorded Investment	5,517	9,700
Interest Income Recognized	179	270
Residential 1-4 Family [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,393	3,110
Unpaid Principal Balance	1,378	3,061
Related Allowance	208	376
Average Recorded Investment	1,522	2,444
Interest Income Recognized	61	175
Residential 1-4 Family [Member] | With No Related Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	629	1,891
Unpaid Principal Balance	622	1,854
Average Recorded Investment	754	1,081
Interest Income Recognized	29	114
Residential 1-4 Family [Member] | With Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	764	1,219
Unpaid Principal Balance	756	1,207
Related Allowance	208	376
Average Recorded Investment	768	1,363
Interest Income Recognized	32	61
Multifamily [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Multifamily [Member] | With No Related Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Multifamily [Member] | With Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	8,713	6,483
Unpaid Principal Balance	10,406	8,999
Related Allowance	711	1,135
Average Recorded Investment	9,741	11,739
Interest Income Recognized	152	297
Commercial Real Estate [Member] | With No Related Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	4,293	1,352
Unpaid Principal Balance	4,293	2,188
Average Recorded Investment	5,183	5,984
Interest Income Recognized	5	95
Commercial Real Estate [Member] | With Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	4,420	5,131
Unpaid Principal Balance	6,113	6,811
Related Allowance	711	1,135
Average Recorded Investment	4,558	5,755
Interest Income Recognized	147	202
Construction [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	2,488
Interest Income Recognized	0	0
Construction [Member] | With No Related Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Average Recorded Investment	0	673
Interest Income Recognized	0	0
Construction [Member] | With Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	1,815
Interest Income Recognized	0	0
Farmland [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	575	702
Unpaid Principal Balance	575	701
Related Allowance	0	120
Average Recorded Investment	574	767
Interest Income Recognized	0	7
Farmland [Member] | With No Related Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	575	0
Unpaid Principal Balance	575	0
Average Recorded Investment	383	0
Interest Income Recognized	0	0
Farmland [Member] | With Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	702
Unpaid Principal Balance	0	701
Related Allowance	0	120
Average Recorded Investment	191	767
Interest Income Recognized	0	7
Second Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	281
Unpaid Principal Balance	0	280
Related Allowance	0	0
Average Recorded Investment	0	222
Interest Income Recognized	0	3
Second Mortgages [Member] | With No Related Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	281
Unpaid Principal Balance	0	280
Average Recorded Investment	0	222
Interest Income Recognized	0	3
Second Mortgages [Member] | With Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Equity Lines of Credit [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Equity Lines of Credit [Member] | With No Related Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Equity Lines of Credit [Member] | With Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Commercial [Member] | With No Related Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Commercial [Member] | With Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0	0
Unpaid Principal Balance	0	0
Related Allowance	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0
Unpaid Principal Balance	0
Related Allowance	0
Average Recorded Investment	0
Interest Income Recognized	0
Agricultural [Member] | With No Related Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0
Unpaid Principal Balance	0
Average Recorded Investment	0
Interest Income Recognized	0
Agricultural [Member] | With Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	0
Unpaid Principal Balance	0
Related Allowance	0
Average Recorded Investment	0
Interest Income Recognized	$ 0
Agricultural, Installment and Other [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		0
Unpaid Principal Balance		0
Related Allowance		0
Average Recorded Investment		0
Interest Income Recognized		0
Agricultural, Installment and Other [Member] | With No Related Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		0
Unpaid Principal Balance		0
Average Recorded Investment		0
Interest Income Recognized		0
Agricultural, Installment and Other [Member] | With Allowance Recorded [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment		0
Unpaid Principal Balance		0
Related Allowance		0
Average Recorded Investment		0
Interest Income Recognized		$ 0