Loans - Past Due, Non-Accrual and Current Non-Covered Loans by Loan Portfolio Class (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	$ 37,508	$ 62,100
Total Past Due Loans	94,221	88,240
Current Non-PCI Loans	15,370,380	13,714,396
Total Non-PCI Loans	15,464,601	13,802,636
30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	34,878	18,509
60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	18,363	5,575
Accruing Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	3,472	2,056
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	8,465	10,913
Total Past Due Loans	20,322	15,570
Current Non-PCI Loans	2,336,696	2,140,979
Total Non-PCI Loans	2,357,018	2,156,549
Commercial and industrial | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	6,705	3,920
Commercial and industrial | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	5,010	524
Commercial and industrial | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	142	213
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	15,794	31,051
Total Past Due Loans	37,987	38,541
Current Non-PCI Loans	8,300,607	6,638,685
Total Non-PCI Loans	8,338,594	6,677,226
Commercial real estate | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	11,971	4,560
Commercial real estate | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	8,642	2,799
Commercial real estate | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,580	131
Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	15,079	24,888
Total Past Due Loans	30,089	27,703
Current Non-PCI Loans	7,598,239	6,041,829
Total Non-PCI Loans	7,628,328	6,069,532
Commercial real estate | Commercial real estate | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	5,894	2,684
Commercial real estate | Commercial real estate | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	8,642	0
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	474	131
Commercial real estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	715	6,163
Total Past Due Loans	7,898	10,838
Current Non-PCI Loans	702,368	596,856
Total Non-PCI Loans	710,266	607,694
Commercial real estate | Construction | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	6,077	1,876
Commercial real estate | Construction | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	2,799
Commercial real estate | Construction | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,106	0
Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	12,075	17,930
Total Past Due Loans	29,185	27,741
Current Non-PCI Loans	2,655,010	2,884,338
Total Non-PCI Loans	2,684,195	2,912,079
Residential mortgage | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	12,005	6,681
Residential mortgage | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	3,564	1,626
Residential mortgage | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,541	1,504
Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	1,174	2,206
Total Past Due Loans	6,727	6,388
Current Non-PCI Loans	2,078,067	2,050,394
Total Non-PCI Loans	2,084,794	2,056,782
Consumer loans | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	4,197	3,348
Consumer loans | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	1,147	626
Consumer loans | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	209	208
Consumer loans | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	1,028	2,088
Total Past Due Loans	2,372	3,507
Current Non-PCI Loans	373,841	388,302
Total Non-PCI Loans	376,213	391,809
Consumer loans | Home equity | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	929	1,308
Consumer loans | Home equity | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	415	111
Consumer loans | Home equity | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	0	0
Consumer loans | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	146	118
Total Past Due Loans	4,249	2,742
Current Non-PCI Loans	1,134,833	1,236,084
Total Non-PCI Loans	1,139,082	1,238,826
Consumer loans | Automobile | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	3,192	1,969
Consumer loans | Automobile | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	723	491
Consumer loans | Automobile | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	188	164
Consumer loans | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Accrual Loans	0	0
Total Past Due Loans	106	139
Current Non-PCI Loans	569,393	426,008
Total Non-PCI Loans	569,499	426,147
Consumer loans | Other consumer | 30-59 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	76	71
Consumer loans | Other consumer | 60-89 Days Past Due Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	9	24
Consumer loans | Other consumer | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	$ 21	$ 44