Loans - Past Due, Non-Accrual and Current Non-Covered Loans by Loan Portfolio Class (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Non-Accrual Loans	$ 93,058	$ 88,396
Total Past Due Loans	161,284	156,101
Current Non-PCI Loans	22,908,325	20,689,282
Total Non-PCI Loans	23,069,609	20,845,383
30-59 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	46,593	51,751
60-89 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	14,315	8,142
Accruing Loans 90 Days Or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due Loans	7,318	7,812
Commercial and industrial
Financing Receivable, Past Due [Line Items]
Non-Accrual Loans	68,636	70,096
Total Past Due Loans	86,549	93,105
Current Non-PCI Loans	4,057,434	3,497,270
Total Non-PCI Loans	4,143,983	3,590,375
Commercial and industrial | 30-59 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	11,700	13,085
Commercial and industrial | 60-89 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	2,227	3,768
Commercial and industrial | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due Loans	3,986	6,156
Commercial real estate
Financing Receivable, Past Due [Line Items]
Non-Accrual Loans	9,360	2,728
Total Past Due Loans	19,354	15,635
Current Non-PCI Loans	12,379,256	11,019,022
Total Non-PCI Loans	12,398,610	11,034,657
Commercial real estate | 30-59 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	4,046	12,350
Commercial real estate | 60-89 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	5,369	530
Commercial real estate | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due Loans	579	27
Commercial real estate | Commercial real estate
Financing Receivable, Past Due [Line Items]
Non-Accrual Loans	9,004	2,372
Total Past Due Loans	16,169	12,450
Current Non-PCI Loans	10,886,724	9,899,859
Total Non-PCI Loans	10,902,893	9,912,309
Commercial real estate | Commercial real estate | 30-59 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	2,560	9,521
Commercial real estate | Commercial real estate | 60-89 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	4,026	530
Commercial real estate | Commercial real estate | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due Loans	579	27
Commercial real estate | Construction
Financing Receivable, Past Due [Line Items]
Non-Accrual Loans	356	356
Total Past Due Loans	3,185	3,185
Current Non-PCI Loans	1,492,532	1,119,163
Total Non-PCI Loans	1,495,717	1,122,348
Commercial real estate | Construction | 30-59 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	1,486	2,829
Commercial real estate | Construction | 60-89 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	1,343	0
Commercial real estate | Construction | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due Loans	0	0
Residential mortgage
Financing Receivable, Past Due [Line Items]
Non-Accrual Loans	12,858	12,917
Total Past Due Loans	36,235	33,239
Current Non-PCI Loans	3,760,707	3,649,745
Total Non-PCI Loans	3,796,942	3,682,984
Residential mortgage | 30-59 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	17,143	16,576
Residential mortgage | 60-89 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	4,192	2,458
Residential mortgage | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due Loans	2,042	1,288
Consumer loans
Financing Receivable, Past Due [Line Items]
Non-Accrual Loans	2,204	2,655
Total Past Due Loans	19,146	14,122
Current Non-PCI Loans	2,710,928	2,523,245
Total Non-PCI Loans	2,730,074	2,537,367
Consumer loans | 30-59 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	13,704	9,740
Consumer loans | 60-89 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	2,527	1,386
Consumer loans | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due Loans	711	341
Consumer loans | Home equity
Financing Receivable, Past Due [Line Items]
Non-Accrual Loans	1,646	2,156
Total Past Due Loans	2,777	3,068
Current Non-PCI Loans	373,243	368,272
Total Non-PCI Loans	376,020	371,340
Consumer loans | Home equity | 30-59 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	1,051	872
Consumer loans | Home equity | 60-89 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	80	40
Consumer loans | Home equity | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due Loans	0	0
Consumer loans | Automobile
Financing Receivable, Past Due [Line Items]
Non-Accrual Loans	334	80
Total Past Due Loans	14,078	9,660
Current Non-PCI Loans	1,437,274	1,309,546
Total Non-PCI Loans	1,451,352	1,319,206
Consumer loans | Automobile | 30-59 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	11,482	7,973
Consumer loans | Automobile | 60-89 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	1,581	1,299
Consumer loans | Automobile | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due Loans	681	308
Consumer loans | Other consumer
Financing Receivable, Past Due [Line Items]
Non-Accrual Loans	224	419
Total Past Due Loans	2,291	1,394
Current Non-PCI Loans	900,411	845,427
Total Non-PCI Loans	902,702	846,821
Consumer loans | Other consumer | 30-59 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	1,171	895
Consumer loans | Other consumer | 60-89 Days Past Due Loans
Financing Receivable, Past Due [Line Items]
Past Due Loans	866	47
Consumer loans | Other consumer | Accruing Loans 90 Days Or More Past Due
Financing Receivable, Past Due [Line Items]
Past Due Loans	$ 30	$ 33