Loans and Other Repossessed Assets Acquired (Detail) - Loan portfolio by age of delinquency (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2011
30-59 Days Past Due	$ 11,342	$ 12,020	$ 9,581
60-89 Days Past Due	5,740	6,354	5,217
90 Days and Greater Past Due	45,891	45,178	42,000
90 Days and Greater, Accruing	43	121	171
Total Past Due	63,016	63,673	56,969
Current	2,432,308	2,321,784	2,298,365
Total Loans	2,495,324	2,385,457	2,355,334
Residential Loans [Member] | Residential 1-4 Family [Member]
30-59 Days Past Due	1,943	1,796	544
60-89 Days Past Due	857	1,190	1,178
90 Days and Greater Past Due	7,137	4,977	1,595
90 Days and Greater, Accruing	0	0	0
Total Past Due	9,937	7,963	3,317
Current	946,418	967,442	906,590
Total Loans	956,355	975,405	909,907
Residential Loans [Member] | Residential Construction [Member]
30-59 Days Past Due	0	0	0
60-89 Days Past Due	0	0	0
90 Days and Greater Past Due	0	0	0
90 Days and Greater, Accruing	0	0	0
Total Past Due	0	0	0
Current	22,439	15,117	16,431
Total Loans	22,439	15,117	16,431
Residential Loans [Member] | Residential Land [Member]
30-59 Days Past Due	8	511	0
60-89 Days Past Due	39	50	65
90 Days and Greater Past Due	785	1,448	1,140
90 Days and Greater, Accruing	0	0	0
Total Past Due	832	2,009	1,205
Current	51,907	39,603	39,520
Total Loans	52,739	41,612	40,725
Residential Loans [Member]
30-59 Days Past Due	1,951	2,307	544
60-89 Days Past Due	896	1,240	1,243
90 Days and Greater Past Due	7,922	6,425	2,735
90 Days and Greater, Accruing	0	0	0
Total Past Due	10,769	9,972	4,522
Current	1,020,764	1,022,162	962,541
Total Loans	1,031,533	1,032,134	967,063
Commercial Loan [Member] | Commercial Business [Member]
30-59 Days Past Due	761	676	435
60-89 Days Past Due	86	232	433
90 Days and Greater Past Due	1,460	3,665	4,322
90 Days and Greater, Accruing	0	0	0
Total Past Due	2,307	4,573	5,190
Current	116,072	79,241	75,681
Total Loans	118,379	83,814	80,871
Commercial Loan [Member] | Commercial Real Estate [Member]
30-59 Days Past Due	2,380	2,250	2,401
60-89 Days Past Due	1,112	1,264	993
90 Days and Greater Past Due	18,386	17,160	18,400
90 Days and Greater, Accruing	0	0	0
Total Past Due	21,878	20,674	21,794
Current	469,689	435,867	449,502
Total Loans	491,567	456,541	471,296
Commercial Loan [Member] | Commercial Construction [Member]
30-59 Days Past Due	0	0	314
60-89 Days Past Due	0	0	281
90 Days and Greater Past Due	247	573	266
90 Days and Greater, Accruing	0	0	0
Total Past Due	247	573	861
Current	817	15,904	14,190
Total Loans	1,064	16,477	15,051
Commercial Loan [Member] | Commercial Loan [Member]
30-59 Days Past Due	966	743	19
60-89 Days Past Due	607	442	518
90 Days and Greater Past Due	4,058	5,232	6,310
90 Days and Greater, Accruing	0	0	0
Total Past Due	5,631	6,417	6,847
Current	64,478	54,821	60,585
Total Loans	70,109	61,238	67,432
Commercial Loan [Member]
30-59 Days Past Due	4,107	3,669	3,169
60-89 Days Past Due	1,805	1,938	2,225
90 Days and Greater Past Due	24,151	26,630	29,298
90 Days and Greater, Accruing	0	0	0
Total Past Due	30,063	32,237	34,692
Current	651,056	585,833	599,958
Total Loans	681,119	618,070	634,650
Consumer Loan [Member] | Home Equity Loans [Member]
30-59 Days Past Due	2,328	2,599	2,661
60-89 Days Past Due	2,086	1,926	747
90 Days and Greater Past Due	10,049	8,192	6,871
90 Days and Greater, Accruing	0	0	0
Total Past Due	14,463	12,717	10,279
Current	370,201	344,553	358,934
Total Loans	384,664	357,270	369,213
Consumer Loan [Member] | Manufactured Housing [Member]
30-59 Days Past Due	2,479	2,515	1,969
60-89 Days Past Due	762	752	631
90 Days and Greater Past Due	3,355	3,461	2,922
90 Days and Greater, Accruing	0	0	0
Total Past Due	6,596	6,728	5,522
Current	273,504	268,547	270,525
Total Loans	280,100	275,275	276,047
Consumer Loan [Member] | Marine [Member]
30-59 Days Past Due	216	410	863
60-89 Days Past Due	68	187	117
90 Days and Greater Past Due	139	246	47
90 Days and Greater, Accruing	0	0	0
Total Past Due	423	843	1,027
Current	75,313	51,747	54,216
Total Loans	75,736	52,590	55,243
Consumer Loan [Member] | Other Consumer [Member]
30-59 Days Past Due	261	520	375
60-89 Days Past Due	123	311	254
90 Days and Greater Past Due	275	224	127
90 Days and Greater, Accruing	43	121	171
Total Past Due	702	1,176	927
Current	41,470	48,942	52,191
Total Loans	42,172	50,118	53,118
Consumer Loan [Member]
30-59 Days Past Due	5,284	6,044	5,868
60-89 Days Past Due	3,039	3,176	1,749
90 Days and Greater Past Due	13,818	12,123	9,967
90 Days and Greater, Accruing	43	121	171
Total Past Due	22,184	21,464	17,755
Current	760,488	713,789	735,866
Total Loans	782,672	735,253	753,621
Acquired non-covered loans [Member]
30-59 Days Past Due	153	0	0
60-89 Days Past Due	329	0	0
90 Days and Greater Past Due	328	0	0
90 Days and Greater, Accruing	0	0	0
Total Past Due	810	0	0
Current	117,321	0	0
Total Loans	118,131	0	0
Acquired covered loans [Member]
30-59 Days Past Due	1,472	1,018	1,834
60-89 Days Past Due	173	1,285	861
90 Days and Greater Past Due	8,649	16,789	18,245
90 Days and Greater, Accruing	0	0	0
Total Past Due	10,294	19,092	20,940
Current	206,395	122,294	133,334
Total Loans	216,689	141,386	154,274
Legacy loans [Member]
30-59 Days Past Due	9,717	11,002	7,747
60-89 Days Past Due	5,238	5,069	4,356
90 Days and Greater Past Due	36,914	28,389	23,755
90 Days and Greater, Accruing	43	121	171
Total Past Due	51,912	44,581	36,029
Current	2,108,592	2,199,490	2,165,031
Total Loans	$ 2,160,504	$ 2,244,071	$ 2,201,060