Loans - Past Due, Non-Accrual and Current Non-Covered Loans by Loan Portfolio Class (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	$ 47,879	$ 62,100
Total Past Due Loans	81,174	88,240
Current Non-PCI Loans	14,442,605	13,714,396
Total Non-PCI Loans	14,523,779	13,802,636
30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	22,975	18,509
60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	9,518	5,575
Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	802	2,056
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	6,573	10,913
Total Past Due Loans	17,692	15,570
Current Non-PCI Loans	2,183,146	2,140,979
Total Non-PCI Loans	2,200,838	2,156,549
Commercial and industrial | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	5,187	3,920
Commercial and industrial | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	5,714	524
Commercial and industrial | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	218	213
Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	25,310	31,051
Total Past Due Loans	31,351	38,541
Current Non-PCI Loans	7,423,631	6,638,685
Total Non-PCI Loans	7,454,982	6,677,226
Commercial real estate loans | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	19,432	24,888
Total Past Due Loans	25,473	27,703
Current Non-PCI Loans	6,797,177	6,041,829
Total Non-PCI Loans	6,822,650	6,069,532
Commercial real estate loans | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	5,878	6,163
Total Past Due Loans	5,878	10,838
Current Non-PCI Loans	626,454	596,856
Total Non-PCI Loans	632,332	607,694
Commercial real estate loans | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	5,076	4,560
Commercial real estate loans | 30-59 Days Past Due Loans | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	5,076	2,684
Commercial real estate loans | 30-59 Days Past Due Loans | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	1,876
Commercial real estate loans | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	834	2,799
Commercial real estate loans | 60-89 Days Past Due Loans | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	834	0
Commercial real estate loans | 60-89 Days Past Due Loans | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	2,799
Commercial real estate loans | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	131	131
Commercial real estate loans | Accruing Loans 90 Days or More Past Due | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	131	131
Commercial real estate loans | Accruing Loans 90 Days or More Past Due | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	0
Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	14,866	17,930
Total Past Due Loans	27,683	27,741
Current Non-PCI Loans	2,829,507	2,884,338
Total Non-PCI Loans	2,857,190	2,912,079
Residential mortgage | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	10,177	6,681
Residential mortgage | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,326	1,626
Residential mortgage | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	314	1,504
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	1,130	2,206
Total Past Due Loans	4,448	6,388
Current Non-PCI Loans	2,006,321	2,050,394
Total Non-PCI Loans	2,010,769	2,056,782
Consumer | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	989	2,088
Total Past Due Loans	2,002	3,507
Current Non-PCI Loans	378,198	388,302
Total Non-PCI Loans	380,200	391,809
Consumer | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	141	118
Total Past Due Loans	2,397	2,742
Current Non-PCI Loans	1,139,113	1,236,084
Total Non-PCI Loans	1,141,510	1,238,826
Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	0	0
Total Past Due Loans	49	139
Current Non-PCI Loans	489,010	426,008
Total Non-PCI Loans	489,059	426,147
Consumer | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,535	3,348
Consumer | 30-59 Days Past Due Loans | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	959	1,308
Consumer | 30-59 Days Past Due Loans | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,552	1,969
Consumer | 30-59 Days Past Due Loans | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	24	71
Consumer | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	644	626
Consumer | 60-89 Days Past Due Loans | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	54	111
Consumer | 60-89 Days Past Due Loans | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	577	491
Consumer | 60-89 Days Past Due Loans | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	13	24
Consumer | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	139	208
Consumer | Accruing Loans 90 Days or More Past Due | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	0
Consumer | Accruing Loans 90 Days or More Past Due | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	127	164
Consumer | Accruing Loans 90 Days or More Past Due | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	$ 12	$ 44