Allowance for Loan Losses - Company's Distribution of Risk Ratings within Held-for-Investment Loan Portfolio (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	$ 1,610,475	$ 1,609,918	$ 1,577,898
Pass [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	1,602,753	1,603,079
Substandard [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	7,722	6,839
Commercial and Industrial [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	230,306	235,946	222,828
Commercial and Industrial [Member] | Pass [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	228,260	233,907
Commercial and Industrial [Member] | Substandard [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	2,046	2,039
Commercial Real Estate Owner Occupied
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	261,971	231,348
Commercial Real Estate Owner Occupied | Pass [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	260,285	229,635
Commercial Real Estate Owner Occupied | Substandard [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	1,686	1,713
Commercial Real Estate Non-Owner Occupied
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	729,102	742,662
Commercial Real Estate Non-Owner Occupied | Pass [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	728,598	742,146
Commercial Real Estate Non-Owner Occupied | Substandard [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	504	516
Land and Development [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	67,336	67,165	86,520
Land and Development [Member] | Pass [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	67,336	67,165
Home Equity Lines of Credit [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	105,885	110,377
Home Equity Lines of Credit [Member] | Pass [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	105,817	110,377
Home Equity Lines of Credit [Member] | Substandard [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	68
Home Equity Term Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	8,405	9,104
Home Equity Term Loans [Member] | Pass [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	8,337	9,032
Home Equity Term Loans [Member] | Substandard [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	68	72
Residential Real Estate Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	205,573	210,874	$ 241,891
Residential Real Estate Loans [Member] | Pass [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	202,223	208,460
Residential Real Estate Loans [Member] | Substandard [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	3,350	2,414
Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	1,897	2,442
Other [Member] | Pass [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment	$ 1,897	2,357
Other [Member] | Substandard [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total gross loans held-for-investment		$ 85