Allowance for Loan Losses - Company's Recorded Investment and Customers' Unpaid Principal Balances for Impaired Loans, with Associated Allowance Amount (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment		$ 5,424	$ 4,224
With no related allowance, Customers' Unpaid Principal Balance		5,504	4,271
With an allowance recorded, Recorded Investment		5,402	2,634
With an allowance recorded, Customers' Unpaid Principal Balance		5,689	2,649
With an allowance recorded, Related Allowance		1,534	676
Total Impaired Loans, Recorded Investment		10,826	6,858
Total Impaired Loans, Customers' Unpaid Principal Balance		11,193	6,920
Total Impaired Loans, Related Allowance		1,534	676
With no related allowance, Average Recorded Investment		3,975	3,790
With no related allowance, Interest Income Recognized		123	147
With an allowance recorded, Average Recorded Investment		3,847	2,550
With an allowance recorded, Interest Income Recognized		147	115
Total, Average Recorded Investment		7,822	6,340
Total, Interest Income Recognized		270	262
Construction, Land and Land Development
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment		445	450
With no related allowance, Customers' Unpaid Principal Balance		451	452
With an allowance recorded, Recorded Investment		262	277
With an allowance recorded, Customers' Unpaid Principal Balance		290	292
With an allowance recorded, Related Allowance		120	144
Total Impaired Loans, Recorded Investment		707	727
Total Impaired Loans, Customers' Unpaid Principal Balance		741	744
Total Impaired Loans, Related Allowance		120	144
With no related allowance, Average Recorded Investment		448	451
With no related allowance, Interest Income Recognized			3
With an allowance recorded, Average Recorded Investment		270	168
With an allowance recorded, Interest Income Recognized		5	4
Total, Average Recorded Investment		718	619
Total, Interest Income Recognized		5	7
Residential First Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment		3,130	1,568
With no related allowance, Customers' Unpaid Principal Balance		3,166	1,584
With an allowance recorded, Recorded Investment		2,507	2,173
With an allowance recorded, Customers' Unpaid Principal Balance		2,507	2,173
With an allowance recorded, Related Allowance		308	437
Total Impaired Loans, Recorded Investment		5,637	3,741
Total Impaired Loans, Customers' Unpaid Principal Balance		5,673	3,757
Total Impaired Loans, Related Allowance		308	437
With no related allowance, Average Recorded Investment		2,077	1,148
With no related allowance, Interest Income Recognized		74	49
With an allowance recorded, Average Recorded Investment		1,900	2,184
With an allowance recorded, Interest Income Recognized		90	100
Total, Average Recorded Investment		3,977	3,332
Total, Interest Income Recognized		164	149
Residential Revolving and Junior Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment	[1]	233	50
With no related allowance, Customers' Unpaid Principal Balance	[1]	233	50
With an allowance recorded, Recorded Investment	[1]	258	173
With an allowance recorded, Customers' Unpaid Principal Balance	[1]	259	173
With an allowance recorded, Related Allowance	[1]	150	84
Total Impaired Loans, Recorded Investment	[1]	491	223
Total Impaired Loans, Customers' Unpaid Principal Balance	[1]	492	223
Total Impaired Loans, Related Allowance	[1]	150	84
With no related allowance, Average Recorded Investment	[1]	87	10
With no related allowance, Interest Income Recognized	[1]	5
With an allowance recorded, Average Recorded Investment	[1]	204	174
With an allowance recorded, Interest Income Recognized	[1]	11	9
Total, Average Recorded Investment	[1]	291	184
Total, Interest Income Recognized	[1]	16	9
Commercial Mortgages (Non-Owner Occupied)
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment		264	264
With no related allowance, Customers' Unpaid Principal Balance		264	264
Total Impaired Loans, Recorded Investment		264	264
Total Impaired Loans, Customers' Unpaid Principal Balance		264	264
With no related allowance, Average Recorded Investment		264	264
With no related allowance, Interest Income Recognized		16	16
Total, Average Recorded Investment		264	264
Total, Interest Income Recognized		16	16
Commercial Mortgages (Owner Occupied)
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment		1,352	1,887
With no related allowance, Customers' Unpaid Principal Balance		1,390	1,916
With an allowance recorded, Recorded Investment		2,091
With an allowance recorded, Customers' Unpaid Principal Balance		2,348
With an allowance recorded, Related Allowance		678
Total Impaired Loans, Recorded Investment		3,443	1,887
Total Impaired Loans, Customers' Unpaid Principal Balance		3,738	1,916
Total Impaired Loans, Related Allowance		678
With no related allowance, Average Recorded Investment		1,099	1,911
With no related allowance, Interest Income Recognized		28	79
With an allowance recorded, Average Recorded Investment		1,343
With an allowance recorded, Interest Income Recognized		39
Total, Average Recorded Investment		2,442	1,911
Total, Interest Income Recognized		67	79
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
With an allowance recorded, Recorded Investment		284
With an allowance recorded, Customers' Unpaid Principal Balance		285
With an allowance recorded, Related Allowance		278
Total Impaired Loans, Recorded Investment		284
Total Impaired Loans, Customers' Unpaid Principal Balance		285
Total Impaired Loans, Related Allowance		278
With an allowance recorded, Average Recorded Investment		130
With an allowance recorded, Interest Income Recognized		2
Total, Average Recorded Investment		130
Total, Interest Income Recognized		$ 2
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
With no related allowance, Recorded Investment	[2]		5
With no related allowance, Customers' Unpaid Principal Balance	[2]		5
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]		16
Total Impaired Loans, Customers' Unpaid Principal Balance	[2]		16
Total Impaired Loans, Related Allowance	[2]		11
With no related allowance, Average Recorded Investment	[2]		6
With an allowance recorded, Average Recorded Investment	[2]		24
With an allowance recorded, Interest Income Recognized	[2]		2
Total, Average Recorded Investment	[2]		30
Total, Interest Income Recognized	[2]		$ 2

[1] Junior mortgages include equity lines.

[2] Includes credit cards.