Loans and Allowances for Credit Losses, By Aging Category (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Accruing	$ 119,132	$ 88,718
Current and Past Due Performing Loans	20,205,680	23,007,520
30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	43,102	68,013
60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	27,870	38,782
90 Days or More [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	153,861	182,227
Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	19,980,847	22,718,498
Commercial [Member]
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Accruing	199	4,821
Current and Past Due Performing Loans	12,506,465	13,077,535
Commercial [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	9,904	17,219
Commercial [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	9,333	10,504
Commercial [Member] | 90 Days or More [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	14,298	71,011
Commercial [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	12,472,930	12,978,801
Commercial [Member] | Energy [Member]
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Accruing	0	0
Current and Past Due Performing Loans	3,006,884	3,469,194
Commercial [Member] | Energy [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	545	12,735
Commercial [Member] | Energy [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	3,716	4,050
Commercial [Member] | Energy [Member] | 90 Days or More [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	0	41,414
Commercial [Member] | Energy [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	3,002,623	3,410,995
Commercial [Member] | Healthcare [Member]
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Accruing	0	0
Current and Past Due Performing Loans	3,414,940	3,305,990
Commercial [Member] | Healthcare [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	2,359	0
Commercial [Member] | Healthcare [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	0	0
Commercial [Member] | Healthcare [Member] | 90 Days or More [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	509	3,645
Commercial [Member] | Healthcare [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	3,412,072	3,302,345
Commercial [Member] | Services [Member]
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Accruing	0	326
Current and Past Due Performing Loans	3,367,193	3,508,583
Commercial [Member] | Services [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	920	3,278
Commercial [Member] | Services [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	4,620	177
Commercial [Member] | Services [Member] | 90 Days or More [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	9,014	15,705
Commercial [Member] | Services [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	3,352,639	3,489,423
Commercial [Member] | General business [Member]
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Accruing	199	4,495
Current and Past Due Performing Loans	2,717,448	2,793,768
Commercial [Member] | General business [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	6,080	1,206
Commercial [Member] | General business [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	997	6,277
Commercial [Member] | General business [Member] | 90 Days or More [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	4,775	10,247
Commercial [Member] | General business [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	2,705,596	2,776,038
Commercial real estate [Member]
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Accruing	0	5,126
Current and Past Due Performing Loans	3,831,325	4,698,538
Commercial real estate [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	0	276
Commercial real estate [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	206	5,310
Commercial real estate [Member] | 90 Days or More [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	3,157	20,673
Commercial real estate [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	3,827,962	4,672,279
Paycheck Protection Program
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Accruing	74	0
Current and Past Due Performing Loans	276,341	1,682,310
Paycheck Protection Program | 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	0	0
Paycheck Protection Program | 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	0	0
Paycheck Protection Program | 90 Days or More [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	0	0
Paycheck Protection Program | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	276,341	1,682,310
Loans to individuals [Member]
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Accruing	118,859	78,771
Current and Past Due Performing Loans	3,591,549	3,549,137
Loans to individuals [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	33,198	50,518
Loans to individuals [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	18,331	22,968
Loans to individuals [Member] | 90 Days or More [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	136,406	90,543
Loans to individuals [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	3,403,614	3,385,108
Loans to individuals [Member] | Residential mortgage [Member]
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Accruing	0	181
Current and Past Due Performing Loans	1,722,170	1,863,003
Loans to individuals [Member] | Residential mortgage [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	6,263	5,812
Loans to individuals [Member] | Residential mortgage [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	1,556	837
Loans to individuals [Member] | Residential mortgage [Member] | 90 Days or More [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	6,697	7,050
Loans to individuals [Member] | Residential mortgage [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	1,707,654	1,849,304
Loans to individuals [Member] | Residential mortgage [Member] | US Government Agency Insured Loans
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Accruing	118,819	78,349
Current and Past Due Performing Loans	354,173	408,687
Loans to individuals [Member] | Residential mortgage [Member] | US Government Agency Insured Loans | 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	26,869	41,389
Loans to individuals [Member] | Residential mortgage [Member] | US Government Agency Insured Loans | 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	16,751	22,041
Loans to individuals [Member] | Residential mortgage [Member] | US Government Agency Insured Loans | 90 Days or More [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	129,531	83,155
Loans to individuals [Member] | Residential mortgage [Member] | US Government Agency Insured Loans | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	181,022	262,102
Loans to individuals [Member] | Personal [Member]
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Accruing	40	241
Current and Past Due Performing Loans	1,515,206	1,277,447
Loans to individuals [Member] | Personal [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	66	3,317
Loans to individuals [Member] | Personal [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	24	90
Loans to individuals [Member] | Personal [Member] | 90 Days or More [Member]
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	178	338
Loans to individuals [Member] | Personal [Member] | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Current and Past Due Performing Loans	$ 1,514,938	$ 1,273,702