Loans - Past Due, Non-Accrual and Current Non-Covered Loans by Loan Portfolio Class (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans 90 Days Or More Past Due	$ 3,533	$ 5,478
Non-Accrual Loans	54,678	55,757
Past Due Loans	72,948	86,987
Current Non-PCI Loans	12,835,874	11,665,125
Total Non-PCI Loans	12,908,822	11,752,112
Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans 90 Days Or More Past Due	133	4,037
Non-Accrual Loans	26,535	27,321
Past Due Loans	30,796	40,857
Current Non-PCI Loans	6,274,298	5,488,979
Total Non-PCI Loans	6,305,094	5,529,836
Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans 90 Days Or More Past Due	160	152
Non-Accrual Loans	1,855	2,209
Past Due Loans	5,099	6,107
Current Non-PCI Loans	1,928,466	1,837,198
Total Non-PCI Loans	1,933,565	1,843,305
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans 90 Days Or More Past Due	226	226
Non-Accrual Loans	9,019	8,467
Past Due Loans	10,800	11,425
Current Non-PCI Loans	2,100,232	1,948,502
Total Non-PCI Loans	2,111,032	1,959,927
Commercial real estate | Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans 90 Days Or More Past Due	133	49
Non-Accrual Loans	21,760	22,098
Past Due Loans	25,617	31,198
Current Non-PCI Loans	5,746,196	5,022,544
Total Non-PCI Loans	5,771,813	5,053,742
Construction | Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans 90 Days Or More Past Due	0	3,988
Non-Accrual Loans	4,775	5,223
Past Due Loans	5,179	9,659
Current Non-PCI Loans	528,102	466,435
Total Non-PCI Loans	533,281	476,094
Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans 90 Days Or More Past Due	3,014	1,063
Non-Accrual Loans	17,269	17,760
Past Due Loans	26,253	28,598
Current Non-PCI Loans	2,532,878	2,390,446
Total Non-PCI Loans	2,559,131	2,419,044
Home equity | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans 90 Days Or More Past Due	0	0
Non-Accrual Loans	1,784	2,022
Past Due Loans	2,593	3,065
Current Non-PCI Loans	389,200	397,071
Total Non-PCI Loans	391,793	400,136
Automobile | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans 90 Days Or More Past Due	134	126
Non-Accrual Loans	0	90
Past Due Loans	2,206	2,509
Current Non-PCI Loans	1,195,829	1,142,271
Total Non-PCI Loans	1,198,035	1,144,780
Other consumer | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Accruing Loans 90 Days Or More Past Due	26	26
Non-Accrual Loans	71	97
Past Due Loans	300	533
Current Non-PCI Loans	343,437	297,856
Total Non-PCI Loans	343,737	298,389
30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	10,156	20,198
30-59 Days Past Due Loans | Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,946	9,386
30-59 Days Past Due Loans | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,440	2,982
30-59 Days Past Due Loans | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,080	1,630
30-59 Days Past Due Loans | Commercial real estate | Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,542	8,938
30-59 Days Past Due Loans | Construction | Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	404	448
30-59 Days Past Due Loans | Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	4,690	6,200
30-59 Days Past Due Loans | Home equity | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	575	761
30-59 Days Past Due Loans | Automobile | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,767	1,902
30-59 Days Past Due Loans | Other consumer | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	98	319
60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	4,581	5,554
60-89 Days Past Due Loans | Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,182	113
60-89 Days Past Due Loans | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	644	764
60-89 Days Past Due Loans | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	475	1,102
60-89 Days Past Due Loans | Commercial real estate | Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,182	113
60-89 Days Past Due Loans | Construction | Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	0
60-89 Days Past Due Loans | Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,280	3,575
60-89 Days Past Due Loans | Home equity | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	234	282
60-89 Days Past Due Loans | Automobile | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	305	391
60-89 Days Past Due Loans | Other consumer | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	$ 105	$ 91