Loans - Summary of Troubled Debt Restructuring by Concessions Made Types (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 20,600	$ 23,900	$ 28,200
Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	61	55	45
Troubled debt restructuring loans	18,015	18,744	22,970
Accruing Loans [Member] | Forbearance of Interest [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	9	2	3
Troubled debt restructuring loans	2,168	1,873	2,092
Accruing Loans [Member] | Forgiveness of Principal [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	3	4
Troubled debt restructuring loans	1,493	1,518	1,897
Accruing Loans [Member] | Payment Modification Only [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	2	1
Troubled debt restructuring loans	373	376	91
Accruing Loans [Member] | Rate Reduction Only [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	12	11	8
Troubled debt restructuring loans	6,924	7,075	6,141
Accruing Loans [Member] | Rate Reduction, Forbearance of Interest [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	18	18	12
Troubled debt restructuring loans	4,724	4,061	8,292
Accruing Loans [Member] | Rate Reduction, Forbearance of Principal [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	17	18	16
Troubled debt restructuring loans	2,333	3,798	4,401
Accruing Loans [Member] | Rate Reduction, Payment Modification [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts		1	1
Troubled debt restructuring loans		43	56
Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	9	5	10
Troubled debt restructuring loans	2,568	5,171	5,170
Non-Accruing Loans [Member] | Forbearance of Interest [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2
Troubled debt restructuring loans	105
Non-Accruing Loans [Member] | Forgiveness of Principal [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	145	372
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	4
Troubled debt restructuring loans	496	177	929
Non-Accruing Loans [Member] | Rate Reduction, Forbearance of Interest [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	2	4
Troubled debt restructuring loans	222	3,420	2,891
Non-Accruing Loans [Member] | Rate Reduction, Forbearance of Principal [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2		1
Troubled debt restructuring loans	1,571		1,099
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