Fair Value Disclosures - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets:
Total available-for-sale securities	$ 328,507	$ 398,518
Investments in equity securities	2,165
Total assets	1,779	1,958
Fair Value Measured on Recurring Basis [Member]
Assets:
Total available-for-sale securities	328,507	391,457
Investments in equity securities	2,165	7,061
Net loans and leases held for investment	1,779	1,958
Total assets	333,130	401,077
Liabilities:
Total liabilities	501	425
Fair Value Measured on Recurring Basis [Member] | Credit Risk Contract [Member]
Liabilities:
Derivative liabilities	72	36
Fair Value Measured on Recurring Basis [Member] | U.S. Government Corporations and Agencies [Member]
Assets:
Total available-for-sale securities	15,315	16,961
Fair Value Measured on Recurring Basis [Member] | State and Political Subdivisions [Member]
Assets:
Total available-for-sale securities	65,415	78,297
Fair Value Measured on Recurring Basis [Member] | Residential Mortgage-Backed Securities [Member]
Assets:
Total available-for-sale securities	151,762	185,421
Fair Value Measured on Recurring Basis [Member] | Collateralized Mortgage Obligations [Member]
Assets:
Total available-for-sale securities	2,888	3,602
Fair Value Measured on Recurring Basis [Member] | Corporate Bonds [Member]
Assets:
Total available-for-sale securities	93,127	107,176
Fair Value Measured on Recurring Basis [Member] | Money Market Mutual Funds [Member]
Assets:
Total available-for-sale securities	924	1,076
Fair Value Measured on Recurring Basis [Member] | Equity Securities [Member]
Assets:
Total available-for-sale securities	1,241	5,985
Fair Value Measured on Recurring Basis [Member] | Interest Rate Locks with Customers [Member]
Assets:
Derivative assets	490	527
Fair Value Measured on Recurring Basis [Member] | Contingent Consideration Liability [Member]
Liabilities:
Derivative liabilities	259	339
Fair Value Measured on Recurring Basis [Member] | Interest Rate Swap [Member]
Assets:
Derivative assets	189	13
Liabilities:
Derivative liabilities	20	50
Fair Value Measured on Recurring Basis [Member] | Forward Loan Sale Commitments [Member]
Assets:
Derivative assets		61
Liabilities:
Derivative liabilities	150
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member]
Assets:
Total available-for-sale securities	0	0
Investments in equity securities	2,165	7,061
Net loans and leases held for investment	0	0
Total assets	2,165	7,061
Liabilities:
Total liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Credit Risk Contract [Member]
Liabilities:
Derivative liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | U.S. Government Corporations and Agencies [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | State and Political Subdivisions [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Residential Mortgage-Backed Securities [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Collateralized Mortgage Obligations [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Corporate Bonds [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Money Market Mutual Funds [Member]
Assets:
Total available-for-sale securities	924	1,076
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Equity Securities [Member]
Assets:
Total available-for-sale securities	1,241	5,985
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Interest Rate Locks with Customers [Member]
Assets:
Derivative assets	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Contingent Consideration Liability [Member]
Liabilities:
Derivative liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Interest Rate Swap [Member]
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Forward Loan Sale Commitments [Member]
Assets:
Derivative assets		0
Liabilities:
Derivative liabilities	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member]
Assets:
Total available-for-sale securities	302,778	363,471
Investments in equity securities	0	0
Net loans and leases held for investment	0	0
Total assets	303,457	364,072
Liabilities:
Total liabilities	170	50
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Credit Risk Contract [Member]
Liabilities:
Derivative liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | U.S. Government Corporations and Agencies [Member]
Assets:
Total available-for-sale securities	15,315	16,961
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | State and Political Subdivisions [Member]
Assets:
Total available-for-sale securities	65,415	78,297
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Residential Mortgage-Backed Securities [Member]
Assets:
Total available-for-sale securities	151,762	185,421
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Collateralized Mortgage Obligations [Member]
Assets:
Total available-for-sale securities	2,888	3,602
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Corporate Bonds [Member]
Assets:
Total available-for-sale securities	67,398	79,190
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Money Market Mutual Funds [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Equity Securities [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Interest Rate Locks with Customers [Member]
Assets:
Derivative assets	490	527
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Contingent Consideration Liability [Member]
Liabilities:
Derivative liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Interest Rate Swap [Member]
Assets:
Derivative assets	189	13
Liabilities:
Derivative liabilities	20	50
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Forward Loan Sale Commitments [Member]
Assets:
Derivative assets		61
Liabilities:
Derivative liabilities	150
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member]
Assets:
Total available-for-sale securities	25,729	27,986
Investments in equity securities	0	0
Net loans and leases held for investment	1,779	1,958
Total assets	27,508	29,944
Liabilities:
Total liabilities	331	375
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Credit Risk Contract [Member]
Liabilities:
Derivative liabilities	72	36
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | U.S. Government Corporations and Agencies [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | State and Political Subdivisions [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Residential Mortgage-Backed Securities [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Collateralized Mortgage Obligations [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Corporate Bonds [Member]
Assets:
Total available-for-sale securities	25,729	27,986
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Money Market Mutual Funds [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Equity Securities [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Interest Rate Locks with Customers [Member]
Assets:
Derivative assets	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Contingent Consideration Liability [Member]
Liabilities:
Derivative liabilities	259	339
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Interest Rate Swap [Member]
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Forward Loan Sale Commitments [Member]
Assets:
Derivative assets		$ 0
Liabilities:
Derivative liabilities	$ 0