Loans - Past Due, Non-Accrual and Current Non-Covered Loans by Loan Portfolio Class (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	$ 38,441	$ 62,100
Total Past Due Loans	77,626	88,240
Current Non-PCI Loans	14,699,394	13,714,396
Total Non-PCI Loans	14,777,020	13,802,636
30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	26,819	18,509
60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	9,046	5,575
Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	3,320	2,056
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	7,875	10,913
Total Past Due Loans	13,114	15,570
Current Non-PCI Loans	2,253,306	2,140,979
Total Non-PCI Loans	2,266,420	2,156,549
Commercial and industrial | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	4,306	3,920
Commercial and industrial | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	788	524
Commercial and industrial | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	145	213
Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	15,588	31,051
Total Past Due Loans	31,623	38,541
Current Non-PCI Loans	7,818,014	6,638,685
Total Non-PCI Loans	7,849,637	6,677,226
Commercial real estate loans | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	14,452	24,888
Total Past Due Loans	28,606	27,703
Current Non-PCI Loans	7,150,230	6,041,829
Total Non-PCI Loans	7,178,836	6,069,532
Commercial real estate loans | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	1,136	6,163
Total Past Due Loans	3,017	10,838
Current Non-PCI Loans	667,784	596,856
Total Non-PCI Loans	670,801	607,694
Commercial real estate loans | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	9,385	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	9,385	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	4,291	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	4,291	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	2,359	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	478	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	1,881	0
Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	14,013	17,930
Total Past Due Loans	27,318	27,741
Current Non-PCI Loans	2,609,993	2,884,338
Total Non-PCI Loans	2,637,311	2,912,079
Residential mortgage | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	9,982	6,681
Residential mortgage | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,733	1,626
Residential mortgage | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	590	1,504
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	965	2,206
Total Past Due Loans	5,571	6,388
Current Non-PCI Loans	2,018,081	2,050,394
Total Non-PCI Loans	2,023,652	2,056,782
Consumer | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	820	2,088
Total Past Due Loans	2,040	3,507
Current Non-PCI Loans	375,642	388,302
Total Non-PCI Loans	377,682	391,809
Consumer | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	145	118
Total Past Due Loans	3,100	2,742
Current Non-PCI Loans	1,118,330	1,236,084
Total Non-PCI Loans	1,121,430	1,238,826
Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	0	0
Total Past Due Loans	431	139
Current Non-PCI Loans	524,109	426,008
Total Non-PCI Loans	524,540	426,147
Consumer | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	3,146	3,348
Consumer | 30-59 Days Past Due Loans | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	693	1,308
Consumer | 30-59 Days Past Due Loans | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,110	1,969
Consumer | 30-59 Days Past Due Loans | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	343	71
Consumer | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,234	626
Consumer | 60-89 Days Past Due Loans | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	527	111
Consumer | 60-89 Days Past Due Loans | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	619	491
Consumer | 60-89 Days Past Due Loans | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	88	24
Consumer | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	226	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	226	164
Consumer | Accruing Loans 90 Days or More Past Due | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	$ 0	$ 44