Loans and Allowance for Credit Losses - Troubled Debt Restructurings Identified During Period (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013 Contract	Jun. 30, 2012 Contract	Jun. 30, 2013 Contract	Jun. 30, 2012 Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts	16	6	32	8
Extend Maturity	$ 373	$ 1,270	$ 806	$ 1,270
Modify Rate	123	18	604	115
Modify Payments	772	6,112	1,302	6,112
Total Pre-Modification Outstanding Recorded Investment	1,268	7,400	2,712	7,497
Post- Modification Outstanding Recorded Investment	1,241	7,391	2,539	7,442
Financing Receivable Specific Reserve				2,760
Specific Reserve	662000	2760000	662000
Recorded Investment			18	0
Number of Contracts			4	0
Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	1	4	3	4
Extend Maturity	100	447	526	447
Modify Rate	0	18	0	18
Modify Payments	0	6,029	12	6,029
Total Pre-Modification Outstanding Recorded Investment	100	6,494	538	6,494
Post- Modification Outstanding Recorded Investment	100	6,494	472	6,494
Financing Receivable Specific Reserve				2,760
Specific Reserve	100	2760	100
Construction Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts		1		1
Extend Maturity		823		823
Modify Rate		0		0
Modify Payments		0		0
Total Pre-Modification Outstanding Recorded Investment		823		823
Post- Modification Outstanding Recorded Investment		815		815
Financing Receivable Specific Reserve				0
Specific Reserve		0
Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	13	1	22	3
Extend Maturity	273	0	280	0
Modify Rate	113	0	326	97
Modify Payments	769	83	1,284	83
Total Pre-Modification Outstanding Recorded Investment	1,155	83	1,890	180
Post- Modification Outstanding Recorded Investment	1,132	82	1,801	133
Financing Receivable Specific Reserve				0
Specific Reserve	562	0	562
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts			1
Extend Maturity			0
Modify Rate			244
Modify Payments			0
Total Pre-Modification Outstanding Recorded Investment			244
Post- Modification Outstanding Recorded Investment			237
Specific Reserve			0
Consumer Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	2		6
Extend Maturity	0		0
Modify Rate	10		34
Modify Payments	3		6
Total Pre-Modification Outstanding Recorded Investment	13		40
Post- Modification Outstanding Recorded Investment	9		29
Specific Reserve	0		0
Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modification, Subsequent Default, Number of Contracts			1
Recorded Investment			9	0
Number of Contracts				0
Consumer Loan [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modification, Subsequent Default, Number of Contracts	2		3
Recorded Investment	$ 5	$ 0	$ 9	$ 0
Number of Contracts		0		0