Fair Value Disclosures - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Assets:
Total available-for-sale securities	$ 329,770,000	$ 314,283,000
Fair Value Measured on Recurring Basis [Member]
Assets:
Total available-for-sale securities	329,770,000	314,283,000
Total assets	330,859,000	315,071,000
Liabilities:
Total liabilities	6,117,000	6,894,000
Fair Value Measured on Recurring Basis [Member] | U.S. Treasuries [Member]
Assets:
Total available-for-sale securities	4,887,000	4,845,000
Fair Value Measured on Recurring Basis [Member] | U.S. Government Corporations and Agencies [Member]
Assets:
Total available-for-sale securities	102,156,000	121,844,000
Fair Value Measured on Recurring Basis [Member] | State and Political Subdivisions [Member]
Assets:
Total available-for-sale securities	102,032,000	102,774,000
Fair Value Measured on Recurring Basis [Member] | Residential Mortgage-Backed Securities [Member]
Assets:
Total available-for-sale securities	13,354,000	13,643,000
Fair Value Measured on Recurring Basis [Member] | Collateralized Mortgage Obligations [Member]
Assets:
Total available-for-sale securities	3,133,000	3,725,000
Fair Value Measured on Recurring Basis [Member] | Corporate Bonds [Member]
Assets:
Total available-for-sale securities	0	54,440,000
Fair Value Measured on Recurring Basis [Member] | Money Market Mutual Funds [Member]
Assets:
Total available-for-sale securities	103,401,000	11,675,000
Fair Value Measured on Recurring Basis [Member] | Equity Securities [Member]
Assets:
Total available-for-sale securities	807,000	1,337,000
Fair Value Measured on Recurring Basis [Member] | Interest Rate Locks with Customers [Member]
Assets:
Interest rate locks with customers	1,089,000	788,000
Fair Value Measured on Recurring Basis [Member] | Contingent Consideration Liability [Member]
Liabilities:
Derivative liabilities	5,577,000	6,541,000
Fair Value Measured on Recurring Basis [Member] | Interest Rate Swap [Member]
Liabilities:
Derivative liabilities	438,000	241,000
Fair Value Measured on Recurring Basis [Member] | Forward Loan Sale Commitments [Member]
Liabilities:
Derivative liabilities	102,000	112,000
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member]
Assets:
Total available-for-sale securities	22,420,000	17,857,000
Total assets	22,420,000	17,857,000
Liabilities:
Total liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | U.S. Treasuries [Member]
Assets:
Total available-for-sale securities	4,887,000	4,845,000
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	16,726,000	11,675,000
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Equity Securities [Member]
Assets:
Total available-for-sale securities	807,000	1,337,000
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Interest Rate Locks with Customers [Member]
Assets:
Interest rate locks with customers	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]
Liabilities:
Derivative liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member]
Assets:
Total available-for-sale securities	307,350,000	296,426,000
Total assets	308,439,000	297,214,000
Liabilities:
Total liabilities	540,000	353,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | U.S. Treasuries [Member]
Assets:
Total available-for-sale securities	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	102,156,000	121,844,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | State and Political Subdivisions [Member]
Assets:
Total available-for-sale securities	102,032,000	102,774,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Residential Mortgage-Backed Securities [Member]
Assets:
Total available-for-sale securities	13,354,000	13,643,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Collateralized Mortgage Obligations [Member]
Assets:
Total available-for-sale securities	3,133,000	3,725,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Corporate Bonds [Member]
Assets:
Total available-for-sale securities	0	54,440,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Money Market Mutual Funds [Member]
Assets:
Total available-for-sale securities	86,675,000	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:
Interest rate locks with customers	1,089,000	788,000
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	438,000	241,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Forward Loan Sale Commitments [Member]
Liabilities:
Derivative liabilities	102,000	112,000
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member]
Assets:
Total available-for-sale securities	0	0
Total assets	0	0
Liabilities:
Total liabilities	5,577,000	6,541,000
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | U.S. Treasuries [Member]
Assets:
Total available-for-sale securities	0	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	0	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:
Interest rate locks with customers	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Contingent Consideration Liability [Member]
Liabilities:
Derivative liabilities	5,577,000	6,541,000
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]
Liabilities:
Derivative liabilities	$ 0	$ 0