Loans - Allowance for Credit Losses and Recorded Investment in Financing Receivables (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Allowance for credit losses:
Allowance for credit losses, Beginning balance	$ 11,103	$ 10,622
Allowance for credit losses, Charge offs	(1,954)	(9,862)
Allowance for credit losses, Recoveries	1,643	943
Allowance for credit losses, Provision	2,750	9,400
Allowance for credit losses, Ending balance	13,542	11,103
Allowance for credit losses, Ending balance: individually evaluated for impairment	4,348	2,301
Allowance for credit losses, Ending balance: collectively evaluated for impairment	9,194	8,802
Financing receivables, Ending balance	594,562	664,051
Financing receivables, Ending balance individually evaluated for impairment	45,462	47,660
Financing receivables, Ending balance collectively evaluated for impairment	549,100	616,391
Commercial [Member]
Allowance for credit losses:
Allowance for credit losses, Beginning balance	4,168	2,773
Allowance for credit losses, Charge offs	(632)	(604)
Allowance for credit losses, Recoveries	19	118
Allowance for credit losses, Provision	2,121	1,881
Allowance for credit losses, Ending balance	5,676	4,168
Allowance for credit losses, Ending balance: individually evaluated for impairment	2,830	1,051
Allowance for credit losses, Ending balance: collectively evaluated for impairment	2,846	3,117
Financing receivables, Ending balance	169,193	232,276
Financing receivables, Ending balance individually evaluated for impairment	10,251	3,458
Financing receivables, Ending balance collectively evaluated for impairment	158,942	228,818
Commercial Real Estate [Member]
Allowance for credit losses:
Allowance for credit losses, Beginning balance	2,783	3,796
Allowance for credit losses, Charge offs	(230)	(6,541)
Allowance for credit losses, Recoveries	1,216	13
Allowance for credit losses, Provision	(482)	5,515
Allowance for credit losses, Ending balance	3,287	2,783
Allowance for credit losses, Ending balance: individually evaluated for impairment	275	194
Allowance for credit losses, Ending balance: collectively evaluated for impairment	3,012	2,589
Financing receivables, Ending balance	304,256	303,266
Financing receivables, Ending balance individually evaluated for impairment	20,053	29,077
Financing receivables, Ending balance collectively evaluated for impairment	284,203	274,189
Consumer [Member]
Allowance for credit losses:
Allowance for credit losses, Beginning balance	28	33
Allowance for credit losses, Charge offs	(25)	(5)
Allowance for credit losses, Recoveries	1	2
Allowance for credit losses, Provision	38	(2)
Allowance for credit losses, Ending balance	42	28
Allowance for credit losses, Ending balance: individually evaluated for impairment	0	0
Allowance for credit losses, Ending balance: collectively evaluated for impairment	42	28
Financing receivables, Ending balance	4,020	4,771
Financing receivables, Ending balance individually evaluated for impairment	0	0
Financing receivables, Ending balance collectively evaluated for impairment	4,020	4,771
Residential [Member]
Allowance for credit losses:
Allowance for credit losses, Beginning balance	3,335	3,690
Allowance for credit losses, Charge offs	(1,067)	(2,712)
Allowance for credit losses, Recoveries	407	810
Allowance for credit losses, Provision	(156)	1,547
Allowance for credit losses, Ending balance	2,519	3,335
Allowance for credit losses, Ending balance: individually evaluated for impairment	1,243	1,056
Allowance for credit losses, Ending balance: collectively evaluated for impairment	1,276	2,279
Financing receivables, Ending balance	117,093	123,738
Financing receivables, Ending balance individually evaluated for impairment	15,158	15,125
Financing receivables, Ending balance collectively evaluated for impairment	101,935	108,613
Unallocated [Member]
Allowance for credit losses:
Allowance for credit losses, Beginning balance	789	330
Allowance for credit losses, Charge offs	0	0
Allowance for credit losses, Recoveries	0	0
Allowance for credit losses, Provision	1,229	459
Allowance for credit losses, Ending balance	2,018	789
Allowance for credit losses, Ending balance: individually evaluated for impairment	0	0
Allowance for credit losses, Ending balance: collectively evaluated for impairment	2,018	789
Financing receivables, Ending balance	0	0
Financing receivables, Ending balance individually evaluated for impairment	0	0
Financing receivables, Ending balance collectively evaluated for impairment	$ 0	$ 0