Loans and Allowance for Credit Losses - Schedule of Past Due Financing Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 20,297	$ 30,481
60-89 Days Past Due	6,023	5,294
Recorded Investment > 90 Days and Accruing	855	1,077
Nonaccrual	148,317	254,336
Total Past Due	175,492	291,188
Current	4,896,984	4,905,406
Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	2,079	2,691
60-89 Days Past Due	823	515
Recorded Investment > 90 Days and Accruing	41	322
Nonaccrual	27,037	36,766
Total Past Due	29,980	40,294
Current	1,351,236	1,296,526
Commercial Real Estate-Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due		11
60-89 Days Past Due	60
Nonaccrual	6,369	14,304
Total Past Due	6,429	14,315
Current	76,776	84,766
Commercial Real Estate-Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	2,642	3,439
60-89 Days Past Due	653	665
Recorded Investment > 90 Days and Accruing		236
Nonaccrual	58,975	81,525
Total Past Due	62,270	85,865
Current	1,020,291	1,070,937
Consumer Heloc [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	851	961
60-89 Days Past Due	71	15
Recorded Investment > 90 Days and Accruing	125
Nonaccrual	1,467	1,720
Total Past Due	2,514	2,696
Current	246,499	255,418
Consumer Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	3,256	4,070
60-89 Days Past Due	805	881
Recorded Investment > 90 Days and Accruing	145	328
Nonaccrual	1,656	1,980
Total Past Due	5,862	7,259
Current	579,423	518,826
Consumer - Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,596	1,732
60-89 Days Past Due	372	403
Recorded Investment > 90 Days and Accruing	101	110
Nonaccrual	1,818	2,109
Total Past Due	3,887	4,354
Current	92,158	118,302
Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	7,991	14,686
60-89 Days Past Due	2,626	1,874
Recorded Investment > 90 Days and Accruing	369	66
Nonaccrual	10,307	11,986
Total Past Due	21,293	28,612
Current	1,323,057	1,296,091
Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,882	2,891
60-89 Days Past Due	613	941
Recorded Investment > 90 Days and Accruing	74	15
Nonaccrual	40,688	103,946
Total Past Due	43,257	107,793
Current	$ 207,544	$ 264,540