Loans - Summary of Impaired Loans by Loan Class (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Noncancelable Obligations Future Minimum Payments Due [Line Items]
Recorded Investment, With no related allowance recorded	$ 23,627,000	$ 30,397,000
Unpaid Principal Balance, With no related allowance recorded	29,738,000	38,297,000
Related Allowance, With no related allowance recorded	0	0
Recorded Investment, With an allowance recorded	21,835,000	17,263,000
Unpaid Principal Balance, With an allowance recorded	23,058,000	18,132,000
Related Allowance, With an allowance recorded	4,348,000	2,301,000
Impaired loans, Recorded Investment	45,462,000	47,660,000
Impaired loans, Unpaid Principal Balance	52,796,000	56,429,000
Impaired loans, Related Allowance	4,348,000	2,301,000
Commercial [Member]
Noncancelable Obligations Future Minimum Payments Due [Line Items]
Recorded Investment, With no related allowance recorded		109,000
Unpaid Principal Balance, With no related allowance recorded		109,000
Related Allowance, With no related allowance recorded		0
Recorded Investment, With an allowance recorded	10,251,000	3,349,000
Unpaid Principal Balance, With an allowance recorded	10,356,000	3,370,000
Related Allowance, With an allowance recorded	2,830,000	1,051,000
Impaired loans, Recorded Investment	10,251,000	3,458,000
Impaired loans, Unpaid Principal Balance	10,356,000	3,479,000
Impaired loans, Related Allowance	2,830,000	1,051,000
Commercial real estate [Member]
Noncancelable Obligations Future Minimum Payments Due [Line Items]
Impaired loans, Recorded Investment	20,053,000	29,077,000
Impaired loans, Unpaid Principal Balance	23,762,000	34,156,000
Impaired loans, Related Allowance	275,000	194,000
Residential [Member]
Noncancelable Obligations Future Minimum Payments Due [Line Items]
Impaired loans, Recorded Investment	15,158,000	15,125,000
Impaired loans, Unpaid Principal Balance	18,678,000	18,794,000
Impaired loans, Related Allowance	1,243,000	1,056,000
Commercial real estate: Other [Member]
Noncancelable Obligations Future Minimum Payments Due [Line Items]
Recorded Investment, With no related allowance recorded	18,092,000	24,479,000
Unpaid Principal Balance, With no related allowance recorded	21,795,000	29,558,000
Related Allowance, With no related allowance recorded	0	0
Recorded Investment, With an allowance recorded	1,961,000	4,598,000
Unpaid Principal Balance, With an allowance recorded	1,967,000	4,598,000
Related Allowance, With an allowance recorded	275,000	194,000
Residential: 1-4 family [Member]
Noncancelable Obligations Future Minimum Payments Due [Line Items]
Recorded Investment, With no related allowance recorded	5,018,000	5,809,000
Unpaid Principal Balance, With no related allowance recorded	7,423,000	8,630,000
Related Allowance, With no related allowance recorded	0	0
Recorded Investment, With an allowance recorded	8,931,000	8,755,000
Unpaid Principal Balance, With an allowance recorded	10,043,000	9,603,000
Related Allowance, With an allowance recorded	987,000	980,000
Residential: Home equities [Member]
Noncancelable Obligations Future Minimum Payments Due [Line Items]
Recorded Investment, With no related allowance recorded	517,000
Unpaid Principal Balance, With no related allowance recorded	520,000
Related Allowance, With no related allowance recorded	0
Recorded Investment, With an allowance recorded	692,000	561,000
Unpaid Principal Balance, With an allowance recorded	692,000	561,000
Related Allowance, With an allowance recorded	$ 256,000	$ 76,000