Fair Value - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013 Securities	Sep. 30, 2012 Securities	Sep. 30, 2013 Securities	Sep. 30, 2012 Securities	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Transfer of securities from level 1 to level 2	$ 0		$ 0	$ 15,232,000
Number of securities transferred from level 2 to level 1	0	0	0	0
Impaired loans, recorded balance	19,345,000		19,345,000		25,520,000
Impaired loans allowance	3,405,000		3,405,000		1,852,000
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Residential mortgage and asset backed securities		3,148,000
Collateral Dependent Loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired loans, recorded balance	12,143,000		12,143,000		12,535,000
Impaired loans allowance	3,405,000		3,405,000		1,738,000
Impaired loans, additional provisions	$ 704,000	$ 756,000	$ 3,233,000	$ 1,544,000