Allowance for Loan Losses - Company's Recorded Investment and Customers' Unpaid Principal Balances for Impaired Loans, with Associated Allowance Amount (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment		$ 5,703		$ 5,703		$ 4,224
With no related allowance, Customers' Unpaid Principal Balance		5,764		5,764		4,271
With no related allowance, Related Allowance		0		0		0
With an allowance recorded, Recorded Investment		4,067		4,067		2,634
With an allowance recorded, Customers' Unpaid Principal Balance		4,097		4,097		2,649
With an allowance recorded, Related Allowance		923		923		676
Total Impaired Loans, Recorded Investment		9,770		9,770		6,858
Total Impaired Loans, Customers' Unpaid Principal Balance		9,861		9,861		6,920
Total Impaired Loans, Related Allowance		923		923		676
With no related allowance, Average Recorded Investment		4,602	$ 3,674	4,240	$ 3,686
With no related allowance, Interest Income Recognized		51	35	83	73
With an allowance recorded, Average Recorded Investment		3,754	2,686	3,612	2,644
With an allowance recorded, Interest Income Recognized		37	30	70	54
Total, Average Recorded Investment		8,356	6,360	7,852	6,330
Total, Interest Income Recognized		88	65	153	127
Construction, Land and Land Development
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment		448		448		450
With no related allowance, Customers' Unpaid Principal Balance		452		452		452
With no related allowance, Related Allowance		0		0		0
With an allowance recorded, Recorded Investment		270		270		277
With an allowance recorded, Customers' Unpaid Principal Balance		292		292		292
With an allowance recorded, Related Allowance		128		128		144
Total Impaired Loans, Recorded Investment		718		718		727
Total Impaired Loans, Customers' Unpaid Principal Balance		744		744		744
Total Impaired Loans, Related Allowance		128		128		144
With no related allowance, Average Recorded Investment		449	451	449	452
With no related allowance, Interest Income Recognized			1		2
With an allowance recorded, Average Recorded Investment		272	288	274	242
With an allowance recorded, Interest Income Recognized		1	1	2	1
Total, Average Recorded Investment		721	739	723	694
Total, Interest Income Recognized		1	2	2	3
Residential First Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment		1,957		1,957		1,568
With no related allowance, Customers' Unpaid Principal Balance		1,981		1,981		1,584
With no related allowance, Related Allowance		0		0		0
With an allowance recorded, Recorded Investment		2,154		2,154		2,173
With an allowance recorded, Customers' Unpaid Principal Balance		2,154		2,154		2,173
With an allowance recorded, Related Allowance		356		356		437
Total Impaired Loans, Recorded Investment		4,111		4,111		3,741
Total Impaired Loans, Customers' Unpaid Principal Balance		4,135		4,135		3,757
Total Impaired Loans, Related Allowance		356		356		437
With no related allowance, Average Recorded Investment		1,761	1,042	1,696	1,046
With no related allowance, Interest Income Recognized		18	10	36	21
With an allowance recorded, Average Recorded Investment		2,160	2,186	2,164	2,190
With an allowance recorded, Interest Income Recognized		26	26	52	47
Total, Average Recorded Investment		3,921	3,228	3,860	3,236
Total, Interest Income Recognized		44	36	88	68
Residential Revolving and Junior Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment	[1]	50		50		50
With no related allowance, Customers' Unpaid Principal Balance	[1]	50		50		50
With no related allowance, Related Allowance	[1]	0		0		0
With an allowance recorded, Recorded Investment	[1]	173		173		173
With an allowance recorded, Customers' Unpaid Principal Balance	[1]	173		173		173
With an allowance recorded, Related Allowance	[1]	83		83		84
Total Impaired Loans, Recorded Investment	[1]	223		223		223
Total Impaired Loans, Customers' Unpaid Principal Balance	[1]	223		223		223
Total Impaired Loans, Related Allowance	[1]	83		83		84
With no related allowance, Average Recorded Investment	[1]	50		50
With no related allowance, Interest Income Recognized	[1]	1		2
With an allowance recorded, Average Recorded Investment	[1]	173	174	173	174
With an allowance recorded, Interest Income Recognized	[1]	2	2	4	4
Total, Average Recorded Investment	[1]	223	174	223	174
Total, Interest Income Recognized	[1]	3	2	6	4
Commercial Mortgages (Non-Owner Occupied)
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment		1,309		1,309		264
With no related allowance, Customers' Unpaid Principal Balance		1,309		1,309		264
With no related allowance, Related Allowance		0		0		0
Total Impaired Loans, Recorded Investment		1,309		1,309		264
Total Impaired Loans, Customers' Unpaid Principal Balance		1,309		1,309		264
With no related allowance, Average Recorded Investment		786	264	612	264
With no related allowance, Interest Income Recognized		14	4	18	8
Total, Average Recorded Investment		786	264	612	264
Total, Interest Income Recognized		14	4	18	8
Commercial Mortgages (Owner Occupied)
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment		1,936		1,936		1,887
With no related allowance, Customers' Unpaid Principal Balance		1,969		1,969		1,916
With no related allowance, Related Allowance		0		0		0
With an allowance recorded, Recorded Investment		1,348		1,348
With an allowance recorded, Customers' Unpaid Principal Balance		1,356		1,356
With an allowance recorded, Related Allowance		234		234
Total Impaired Loans, Recorded Investment		3,284		3,284		1,887
Total Impaired Loans, Customers' Unpaid Principal Balance		3,325		3,325		1,916
Total Impaired Loans, Related Allowance		234		234
With no related allowance, Average Recorded Investment		1,552	1,917	1,429	1,924
With no related allowance, Interest Income Recognized		18	20	27	42
With an allowance recorded, Average Recorded Investment		1,026		919
With an allowance recorded, Interest Income Recognized		8		12
Total, Average Recorded Investment		2,578	1,917	2,348	1,924
Total, Interest Income Recognized		26	20	39	42
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Related Allowance		0		0		0
With an allowance recorded, Recorded Investment		122		122
With an allowance recorded, Customers' Unpaid Principal Balance		122		122
With an allowance recorded, Related Allowance		122		122
Total Impaired Loans, Recorded Investment		122		122
Total Impaired Loans, Customers' Unpaid Principal Balance		122		122
Total Impaired Loans, Related Allowance		122		122
With an allowance recorded, Average Recorded Investment		123		82
Total, Average Recorded Investment		123		82
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment	[2]	3		3		5
With no related allowance, Customers' Unpaid Principal Balance	[2]	3		3		5
With no related allowance, Related Allowance	[2]	0		0		0
With an allowance recorded, Recorded Investment	[2]					11
With an allowance recorded, Customers' Unpaid Principal Balance	[2]					11
With an allowance recorded, Related Allowance	[2]					11
Total Impaired Loans, Recorded Investment	[2]	3		3		16
Total Impaired Loans, Customers' Unpaid Principal Balance	[2]	3		3		16
Total Impaired Loans, Related Allowance	[2]					$ 11
With no related allowance, Average Recorded Investment	[2]	4		4
With an allowance recorded, Average Recorded Investment	[2]		38		38
With an allowance recorded, Interest Income Recognized	[2]		1		2
Total, Average Recorded Investment	[2]	$ 4	38	$ 4	38
Total, Interest Income Recognized	[2]		$ 1		$ 2

[1] Junior mortgages include equity lines.

[2] Includes credit cards.