Loans and Other Repossessed Assets Acquired (Detail) - Residential Credit Quality (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Performing Financing Receivable [Member] | Residential Loans [Member]
Residential Credit Quality	$ 1,003,139	[1]	$ 998,902	[1]
Performing Financing Receivable [Member] | Residential 1-4 Family [Member]
Residential Credit Quality	934,014	[1]	928,298	[1]
Performing Financing Receivable [Member] | Residential Construction [Member]
Residential Credit Quality	25,895	[1]	22,439	[1]
Performing Financing Receivable [Member] | Residential Land [Member]
Residential Credit Quality	43,230	[1]	48,165	[1]
Performing Classified [Member] | Residential Loans [Member]
Residential Credit Quality	11,372	[1]	10,130	[1]
Performing Classified [Member] | Residential 1-4 Family [Member]
Residential Credit Quality	10,261	[1]	9,598	[1]
Performing Classified [Member] | Residential Construction [Member]
Residential Credit Quality	0	[1]	0	[1]
Performing Classified [Member] | Residential Land [Member]
Residential Credit Quality	1,111	[1]	532	[1]
Nonperforming Financing Receivable [Member] | Residential Loans [Member]
Residential Credit Quality	8,526	[1]	7,922	[1]
Nonperforming Financing Receivable [Member] | Residential 1-4 Family [Member]
Residential Credit Quality	7,693	[1]	7,137	[1]
Nonperforming Financing Receivable [Member] | Residential Construction [Member]
Residential Credit Quality	0	[1]	0	[1]
Nonperforming Financing Receivable [Member] | Residential Land [Member]
Residential Credit Quality	833	[1]	785	[1]
Total Residential Loans [Member] | Residential Loans [Member]
Residential Credit Quality	1,023,037	[1]	1,016,954	[1]
Total Residential Loans [Member] | Residential 1-4 Family [Member]
Residential Credit Quality	951,968	[1]	945,033	[1]
Total Residential Loans [Member] | Residential Construction [Member]
Residential Credit Quality	25,895	[1]	22,439	[1]
Total Residential Loans [Member] | Residential Land [Member]
Residential Credit Quality	45,174	[1]	49,482	[1]
ASC 310-30 Loans [Member] | Residential Loans [Member]
Residential Credit Quality	14,822	[1]	14,579	[1]
ASC 310-30 Loans [Member] | Residential 1-4 Family [Member]
Residential Credit Quality	11,085	[1]	11,322	[1]
ASC 310-30 Loans [Member] | Residential Construction [Member]
Residential Credit Quality	0	[1]	0	[1]
ASC 310-30 Loans [Member] | Residential Land [Member]
Residential Credit Quality	3,737	[1]	3,257	[1]
Residential Loans [Member]
Residential Credit Quality	1,037,859	[1]	1,031,533	[1]
Residential 1-4 Family [Member]
Residential Credit Quality	963,053	[1]	956,355	[1]
Residential Construction [Member]
Residential Credit Quality	25,895	[1]	22,439	[1]
Residential Land [Member]
Residential Credit Quality	$ 48,911	[1]	$ 52,739	[1]

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