Fair Value Disclosures - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Assets:
Total available-for-sale securities	$ 443,637,000	$ 329,770,000
Total assets	2,138,000
Fair Value Measured on Recurring Basis [Member]
Assets:
Total available-for-sale securities	443,637,000	329,770,000
Net loans and leases held for investment	2,138,000
Total assets	446,833,000	330,859,000
Liabilities:
Total liabilities	6,327,000	6,117,000
Fair Value Measured on Recurring Basis [Member] | Credit Risk Contract [Member]
Liabilities:
Derivative liabilities	9,000
Fair Value Measured on Recurring Basis [Member] | U.S. Treasuries [Member]
Assets:
Total available-for-sale securities		4,887,000
Fair Value Measured on Recurring Basis [Member] | U.S. Government Corporations and Agencies [Member]
Assets:
Total available-for-sale securities	32,266,000	102,156,000
Fair Value Measured on Recurring Basis [Member] | State and Political Subdivisions [Member]
Assets:
Total available-for-sale securities	88,350,000	102,032,000
Fair Value Measured on Recurring Basis [Member] | Residential Mortgage-Backed Securities [Member]
Assets:
Total available-for-sale securities	198,570,000	13,354,000
Fair Value Measured on Recurring Basis [Member] | Collateralized Mortgage Obligations [Member]
Assets:
Total available-for-sale securities	4,554,000	3,133,000
Fair Value Measured on Recurring Basis [Member] | Corporate Bonds [Member]
Assets:
Total available-for-sale securities	108,198,000	86,675,000
Fair Value Measured on Recurring Basis [Member] | Money Market Mutual Funds [Member]
Assets:
Total available-for-sale securities	10,784,000	16,726,000
Fair Value Measured on Recurring Basis [Member] | Equity Securities [Member]
Assets:
Total available-for-sale securities	915,000	807,000
Fair Value Measured on Recurring Basis [Member] | Interest Rate Locks with Customers [Member]
Assets:
Derivative assets	801,000	1,089,000
Fair Value Measured on Recurring Basis [Member] | Contingent Consideration Liability [Member]
Liabilities:
Derivative liabilities	5,999,000	5,577,000
Fair Value Measured on Recurring Basis [Member] | Interest Rate Swap [Member]
Liabilities:
Derivative liabilities	319,000	438,000
Fair Value Measured on Recurring Basis [Member] | Forward Loan Sale Commitments [Member]
Assets:
Derivative assets	257,000
Liabilities:
Derivative liabilities		102,000
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member]
Assets:
Total available-for-sale securities	11,699,000	22,420,000
Net loans and leases held for investment	0
Total assets	11,699,000	22,420,000
Liabilities:
Total liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Credit Risk Contract [Member]
Liabilities:
Derivative liabilities	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | U.S. Treasuries [Member]
Assets:
Total available-for-sale securities		4,887,000
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	10,784,000	16,726,000
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Equity Securities [Member]
Assets:
Total available-for-sale securities	915,000	807,000
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]
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	403,160,000	307,350,000
Net loans and leases held for investment	0
Total assets	404,218,000	308,439,000
Liabilities:
Total liabilities	319,000	540,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Credit Risk Contract [Member]
Liabilities:
Derivative liabilities	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | U.S. Treasuries [Member]
Assets:
Total available-for-sale securities		0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | U.S. Government Corporations and Agencies [Member]
Assets:
Total available-for-sale securities	32,266,000	102,156,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | State and Political Subdivisions [Member]
Assets:
Total available-for-sale securities	88,350,000	102,032,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Residential Mortgage-Backed Securities [Member]
Assets:
Total available-for-sale securities	198,570,000	13,354,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Collateralized Mortgage Obligations [Member]
Assets:
Total available-for-sale securities	4,554,000	3,133,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Corporate Bonds [Member]
Assets:
Total available-for-sale securities	79,420,000	86,675,000
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	801,000	1,089,000
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]
Liabilities:
Derivative liabilities	319,000	438,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Forward Loan Sale Commitments [Member]
Assets:
Derivative assets	257,000
Liabilities:
Derivative liabilities		102,000
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member]
Assets:
Total available-for-sale securities	28,778,000	0
Net loans and leases held for investment	2,138,000
Total assets	30,916,000	0
Liabilities:
Total liabilities	6,008,000	5,577,000
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Credit Risk Contract [Member]
Liabilities:
Derivative liabilities	9,000
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | U.S. Treasuries [Member]
Assets:
Total available-for-sale securities		0
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	28,778,000	0
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	5,999,000	5,577,000
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Interest Rate Swap [Member]
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