Loans - Past Due, Non-Accrual and Current Non-Covered Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	$ 42,154	$ 37,508
Total Past Due Loans	83,921	94,221
Current Non-PCI Loans	16,085,370	15,370,380
Total Non-PCI Loans	16,169,291	15,464,601
30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	18,444	34,878
60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	14,501	18,363
Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	8,822	3,472
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	11,072	8,465
Total Past Due Loans	16,149	20,322
Current Non-PCI Loans	2,401,775	2,336,696
Total Non-PCI Loans	2,417,924	2,357,018
Commercial and industrial | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,391	6,705
Commercial and industrial | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,686	5,010
Commercial and industrial | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	142
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	16,848	15,794
Total Past Due Loans	38,112	37,987
Current Non-PCI Loans	8,988,319	8,300,607
Total Non-PCI Loans	9,026,431	8,338,594
Commercial Real Estate | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	6,983	11,971
Commercial Real Estate | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	9,087	8,642
Commercial Real Estate | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	5,194	1,580
Commercial Real Estate | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	15,514	15,079
Total Past Due Loans	33,045	30,089
Current Non-PCI Loans	8,168,190	7,598,239
Total Non-PCI Loans	8,201,235	7,628,328
Commercial Real Estate | Commercial real estate | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	6,983	5,894
Commercial Real Estate | Commercial real estate | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	8,233	8,642
Commercial Real Estate | Commercial real estate | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,315	474
Commercial Real Estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	1,334	715
Total Past Due Loans	5,067	7,898
Current Non-PCI Loans	820,129	702,368
Total Non-PCI Loans	825,196	710,266
Commercial Real Estate | Construction | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	6,077
Commercial Real Estate | Construction | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	854	0
Commercial Real Estate | Construction | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2,879	1,106
Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	12,825	12,075
Total Past Due Loans	22,576	29,185
Current Non-PCI Loans	2,546,924	2,655,010
Total Non-PCI Loans	2,569,500	2,684,195
Residential mortgage | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	4,677	12,005
Residential mortgage | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,721	3,564
Residential mortgage | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	3,353	1,541
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	1,409	1,174
Total Past Due Loans	7,084	6,727
Current Non-PCI Loans	2,148,352	2,078,067
Total Non-PCI Loans	2,155,436	2,084,794
Consumer | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	4,393	4,197
Consumer | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,007	1,147
Consumer | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	275	209
Consumer | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	1,306	1,028
Total Past Due Loans	2,523	2,372
Current Non-PCI Loans	366,849	373,841
Total Non-PCI Loans	369,372	376,213
Consumer | Home equity | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	988	929
Consumer | Home equity | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	229	415
Consumer | Home equity | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	0
Consumer | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	103	146
Total Past Due Loans	4,374	4,249
Current Non-PCI Loans	1,145,843	1,134,833
Total Non-PCI Loans	1,150,217	1,139,082
Consumer | Automobile | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	3,242	3,192
Consumer | Automobile | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	774	723
Consumer | Automobile | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	255	188
Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	0	0
Total Past Due Loans	187	106
Current Non-PCI Loans	635,660	569,393
Total Non-PCI Loans	635,847	569,499
Consumer | Other consumer | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	163	76
Consumer | Other consumer | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	4	9
Consumer | Other consumer | Accruing Loans 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	$ 20	$ 21