Loans - Summary of Troubled Debt Restructuring by Concessions Made Types (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 20,200	$ 23,900	$ 23,300
Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	64	55	51
Troubled debt restructuring loans	17,024	18,744	19,893
Accruing Loans [Member] | Forbearance of Interest [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	9	2	2
Troubled debt restructuring loans	2,135	1,873	1,902
Accruing Loans [Member] | Forgiveness of Principal [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	3	3
Troubled debt restructuring loans	1,479	1,518	1,516
Accruing Loans [Member] | Payment Modification Only [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	2	2
Troubled debt restructuring loans	370	376	1,292
Accruing Loans [Member] | Rate Reduction Only [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	14	11	10
Troubled debt restructuring loans	7,146	7,075	5,889
Accruing Loans [Member] | Rate Reduction, Forbearance of Interest [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	18	18	15
Troubled debt restructuring loans	2,878	4,061	4,371
Accruing Loans [Member] | Rate Reduction, Forbearance of Principal [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	18	18	18
Troubled debt restructuring loans	3,016	3,798	4,874
Accruing Loans [Member] | Rate Reduction, Payment Modification [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts		1	1
Troubled debt restructuring loans		43	49
Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	16	5	3
Troubled debt restructuring loans	3,150	5,171	3,390
Non-Accruing Loans [Member] | Forbearance of Interest [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2
Troubled debt restructuring loans	101
Non-Accruing Loans [Member] | Forgiveness of Principal [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1	1
Troubled debt restructuring loans	145	372	369
Non-Accruing Loans [Member] | Payment Modification Only [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts			1
Troubled debt restructuring loans			251
Non-Accruing Loans [Member] | Rate Reduction Only [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	1
Troubled debt restructuring loans	496	177
Non-Accruing Loans [Member] | Rate Reduction, Forbearance of Interest [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	10	2	1
Troubled debt restructuring loans	2,379	3,420	2,770
Non-Accruing Loans [Member] | Rate Reduction, Forbearance of Principal [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts
Troubled debt restructuring loans
Non-Accruing Loans [Member] | Rate Reduction, Payment Modification [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	$ 29	$ 1,202