Allowance for Loan Losses - Company's Recorded Investment and Customers' Unpaid Principal Balances for Impaired Loans, with Associated Allowance Amount (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment	$ 3,664				$ 3,664				$ 3,912
With no related allowance, Customers' Unpaid Principal Balance	3,697				3,697				3,925
With no related allowance, Related Allowance
With an allowance recorded, Recorded Investment	2,825				2,825				2,744
With an allowance recorded, Customers' Unpaid Principal Balance	2,844				2,844				3,377
With an allowance recorded, Related Allowance	756				756				667
Total Impaired Loans, Recorded Investment	6,489				6,489				6,656
Total Impaired Loans, Customers' Unpaid Principal Balance	6,541				6,541				7,302
Total Impaired Loans, Related Allowance	756				756				667
With no related allowance, Average Recorded Investment	3,674		2,530		3,686		2,435
With no related allowance, Interest Income Recognized	35		32		73		57
With an allowance recorded, Average Recorded Investment	2,686		3,775		2,644		3,655
With an allowance recorded, Interest Income Recognized	30		30		54		60
Total, Average Recorded Investment	6,360		6,305		6,330		6,090
Total, Interest Income Recognized	65		62		127		117
Construction, Land and Land Development
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment	451				451				453
With no related allowance, Customers' Unpaid Principal Balance	453				453				453
With no related allowance, Related Allowance
With an allowance recorded, Recorded Investment	428				428				151
With an allowance recorded, Customers' Unpaid Principal Balance	447				447				156
With an allowance recorded, Related Allowance	211				211				51
Total Impaired Loans, Recorded Investment	879				879				604
Total Impaired Loans, Customers' Unpaid Principal Balance	900				900				609
Total Impaired Loans, Related Allowance	211				211				51
With no related allowance, Average Recorded Investment	451		13		452		13
With no related allowance, Interest Income Recognized	1				2
With an allowance recorded, Average Recorded Investment	288		200		242		200
With an allowance recorded, Interest Income Recognized	1				1
Total, Average Recorded Investment	739		213		694		213
Total, Interest Income Recognized	2				3
Residential First Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment	1,039				1,039				1,053
With no related allowance, Customers' Unpaid Principal Balance	1,049				1,049				1,057
With no related allowance, Related Allowance
With an allowance recorded, Recorded Investment	2,185				2,185				2,198
With an allowance recorded, Customers' Unpaid Principal Balance	2,185				2,185				2,198
With an allowance recorded, Related Allowance	436				436				409
Total Impaired Loans, Recorded Investment	3,224				3,224				3,251
Total Impaired Loans, Customers' Unpaid Principal Balance	3,234				3,234				3,255
Total Impaired Loans, Related Allowance	436				436				409
With no related allowance, Average Recorded Investment	1,042		1,668		1,046		1,570
With no related allowance, Interest Income Recognized	10		24		21		42
With an allowance recorded, Average Recorded Investment	2,186		1,845		2,190		1,778
With an allowance recorded, Interest Income Recognized	26		24		47		50
Total, Average Recorded Investment	3,228		3,513		3,236		3,348
Total, Interest Income Recognized	36		48		68		92
Residential Revolving and Junior Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Related Allowance		[1]				[1]				[1]
With an allowance recorded, Recorded Investment	174	[1]			174	[1]			251	[1]
With an allowance recorded, Customers' Unpaid Principal Balance	174	[1]			174	[1]			879	[1]
With an allowance recorded, Related Allowance	77	[1]			77	[1]			173	[1]
Total Impaired Loans, Recorded Investment	174	[1]			174	[1]			251	[1]
Total Impaired Loans, Customers' Unpaid Principal Balance	174	[1]			174	[1]			879	[1]
Total Impaired Loans, Related Allowance	77	[1]			77	[1]			173	[1]
With no related allowance, Average Recorded Investment			97	[1]			98	[1]
With an allowance recorded, Average Recorded Investment	174	[1]	1,124	[1]	174	[1]	1,068	[1]
With an allowance recorded, Interest Income Recognized	2	[1]	2	[1]	4	[1]	4	[1]
Total, Average Recorded Investment	174	[1]	1,221	[1]	174	[1]	1,166	[1]
Total, Interest Income Recognized	2	[1]	2	[1]	4	[1]	4	[1]
Commercial Mortgages (Non-Owner Occupied)
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment	264				264				264
With no related allowance, Customers' Unpaid Principal Balance	264				264				264
With no related allowance, Related Allowance
Total Impaired Loans, Recorded Investment	264				264				264
Total Impaired Loans, Customers' Unpaid Principal Balance	264				264				264
With no related allowance, Average Recorded Investment	264				264
With no related allowance, Interest Income Recognized	4				8
Total, Average Recorded Investment	264				264
Total, Interest Income Recognized	4				8
Commercial Mortgages (Owner Occupied)
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment	1,910				1,910				1,831
With no related allowance, Customers' Unpaid Principal Balance	1,931				1,931				1,840
With no related allowance, Related Allowance
With an allowance recorded, Recorded Investment									105
With an allowance recorded, Customers' Unpaid Principal Balance									105
With an allowance recorded, Related Allowance									1
Total Impaired Loans, Recorded Investment	1,910				1,910				1,936
Total Impaired Loans, Customers' Unpaid Principal Balance	1,931				1,931				1,945
Total Impaired Loans, Related Allowance									1
With no related allowance, Average Recorded Investment	1,917		752		1,924		754
With no related allowance, Interest Income Recognized	20		8		42		15
With an allowance recorded, Average Recorded Investment			533				536
With an allowance recorded, Interest Income Recognized			3				3
Total, Average Recorded Investment	1,917		1,285		1,924		1,290
Total, Interest Income Recognized	20		11		42		18
Commercial and Industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment									311
With no related allowance, Customers' Unpaid Principal Balance									311
With no related allowance, Related Allowance
Total Impaired Loans, Recorded Investment									311
Total Impaired Loans, Customers' Unpaid Principal Balance									311
Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Related Allowance		[2]				[2]				[2]
With an allowance recorded, Recorded Investment	38	[2]			38	[2]			39	[2]
With an allowance recorded, Customers' Unpaid Principal Balance	38	[2]			38	[2]			39	[2]
With an allowance recorded, Related Allowance	32	[2]			32	[2]			33	[2]
Total Impaired Loans, Recorded Investment	38	[2]			38	[2]			39	[2]
Total Impaired Loans, Customers' Unpaid Principal Balance	38	[2]			38	[2]			39	[2]
Total Impaired Loans, Related Allowance	32	[2]			32	[2]			33	[2]
With an allowance recorded, Average Recorded Investment	38	[2]	73	[2]	38	[2]	73	[2]
With an allowance recorded, Interest Income Recognized	1	[2]	1	[2]	2	[2]	3	[2]
Total, Average Recorded Investment	38	[2]	73	[2]	38	[2]	73	[2]
Total, Interest Income Recognized	$ 1	[2]	$ 1	[2]	$ 2	[2]	$ 3	[2]

[1] Junior mortgages include equity lines.

[2] Includes credit cards.