Loans and Other Repossessed Assets Acquired (Detail) - Schedule of Residential Credit Quality (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011		Sep. 30, 2011
Performing Financing Receivable [Member] | Residential 1-4 Family [Member]
Residential Credit Quality	$ 928,298	[1]	$ 967,193	[1]	$ 906,385	[1]
Performing Financing Receivable [Member] | Residential Construction [Member]
Residential Credit Quality	22,439	[1]	15,117	[1]	16,431	[1]
Performing Financing Receivable [Member] | Residential Land [Member]
Residential Credit Quality	48,165	[1]	39,701	[1]	39,108	[1]
Performing Financing Receivable [Member] | Residential Loans [Member]
Residential Credit Quality	998,902	[1]	1,022,011	[1]	961,924	[1]
Performing Classified [Member] | Residential 1-4 Family [Member]
Residential Credit Quality	9,598	[1]	578	[1]	917	[1]
Performing Classified [Member] | Residential Construction [Member]
Residential Credit Quality	0	[1]	0	[1]	0	[1]
Performing Classified [Member] | Residential Land [Member]
Residential Credit Quality	532	[1]	323	[1]	321	[1]
Performing Classified [Member] | Residential Loans [Member]
Residential Credit Quality	10,130	[1]	901	[1]	1,238	[1]
Nonperforming Financing Receivable [Member] | Residential 1-4 Family [Member]
Residential Credit Quality	7,137	[1]	7,388	[1]	2,329	[1]
Nonperforming Financing Receivable [Member] | Residential Construction [Member]
Residential Credit Quality	0	[1]	0	[1]	0	[1]
Nonperforming Financing Receivable [Member] | Residential Land [Member]
Residential Credit Quality	785	[1]	1,448	[1]	1,140	[1]
Nonperforming Financing Receivable [Member] | Residential Loans [Member]
Residential Credit Quality	7,922	[1]	8,836	[1]	3,469	[1]
Total residential loans [Member] | Residential 1-4 Family [Member]
Residential Credit Quality	945,033	[1]	975,159	[1]	909,631	[1]
Total residential loans [Member] | Residential Construction [Member]
Residential Credit Quality	22,439	[1]	15,117	[1]	16,431	[1]
Total residential loans [Member] | Residential Land [Member]
Residential Credit Quality	49,482	[1]	41,472	[1]	40,569	[1]
Total residential loans [Member] | Residential Loans [Member]
Residential Credit Quality	1,016,954	[1]	1,031,748	[1]	966,631	[1]
ASC-310-30 loans [Member] | Residential 1-4 Family [Member]
Residential Credit Quality	11,322	[1]	246	[1]	276	[1]
ASC-310-30 loans [Member] | Residential Construction [Member]
Residential Credit Quality	0	[1]	0	[1]	0	[1]
ASC-310-30 loans [Member] | Residential Land [Member]
Residential Credit Quality	3,257	[1]	140	[1]	156	[1]
ASC-310-30 loans [Member] | Residential Loans [Member]
Residential Credit Quality	14,579	[1]	386	[1]	432	[1]
Residential 1-4 Family [Member]
Residential Credit Quality	956,355	[1]	975,405	[1]	909,907	[1]
Residential Construction [Member]
Residential Credit Quality	22,439	[1]	15,117	[1]	16,431	[1]
Residential Land [Member]
Residential Credit Quality	52,739	[1]	41,612	[1]	40,725	[1]
Residential Loans [Member]
Residential Credit Quality	$ 1,031,533	[1]	$ 1,032,134	[1]	$ 967,063	[1]

[1] Credit quality indicators are reviewed and updated as applicable on an ongoing basis in accordance with credit policies.