Loans and Allowance for Credit Losses - Schedule of Past Due Financing Receivables (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 16,482	$ 22,461
60-89 Days Past Due	4,655	8,024
Recorded Investment > 90 Days and Accruing	598	458
Nonaccrual	167,802	140,857
Total Past Due	189,537	171,800
Current	6,576,525	6,146,401
Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	704	649
60-89 Days Past Due	1,107	813
Recorded Investment > 90 Days and Accruing	325	33
Nonaccrual	70,665	38,460
Total Past Due	72,801	39,955
Current	1,703,153	1,589,645
Commercial Real Estate - Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	4,212	6,499
Total Past Due	4,212	6,499
Current	159,702	128,053
Commercial Real Estate - Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,005	3,834
60-89 Days Past Due	301	1,468
Recorded Investment > 90 Days and Accruing		138
Nonaccrual	62,038	60,903
Total Past Due	63,344	66,343
Current	1,540,083	1,510,215
Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	10,055	11,606
60-89 Days Past Due	1,878	3,959
Recorded Investment > 90 Days and Accruing	88	1
Nonaccrual	14,058	13,968
Total Past Due	26,079	29,534
Current	1,596,740	1,489,622
Consumer Heloc [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	566	577
60-89 Days Past Due	196	376
Nonaccrual	2,716	3,115
Total Past Due	3,478	4,068
Current	366,483	356,252
Consumer Auto [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	2,995	3,349
60-89 Days Past Due	592	695
Recorded Investment > 90 Days and Accruing	27	203
Nonaccrual	1,243	1,261
Total Past Due	4,857	5,508
Current	951,002	841,461
Consumer - Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	500	969
60-89 Days Past Due	174	129
Recorded Investment > 90 Days and Accruing	158	83
Nonaccrual	1,430	1,527
Total Past Due	2,262	2,708
Current	136,459	100,630
Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	657	1,477
60-89 Days Past Due	407	584
Nonaccrual	11,440	15,124
Total Past Due	12,504	17,185
Current	$ 122,903	$ 130,523