Loans and Allowances for Credit Losses, By Aging Category (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing receivable, recorded investment, aging [Abstract]
Current	$ 23,383,412	$ 21,392,306
Nonaccrual	221,153	180,951
Total	23,803,300	21,750,987
Past Due 90 Days or More and Accruing	124,872	7,680
30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	119,679	47,084
60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	42,045	20,560
90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	258,164	110,086
Commercial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	13,397,500	13,899,429
Nonaccrual	169,953	115,416
Total	13,565,706	14,031,650
Past Due 90 Days or More and Accruing	672
Commercial [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	52,988	7,943
Commercial [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	5,510	1,608
Commercial [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	109,708	7,254
Commercial [Member] | Energy [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	3,603,548	3,881,244
Nonaccrual	126,816	91,722
Total	3,717,101	3,973,377
Past Due 90 Days or More and Accruing	0
Commercial [Member] | Energy [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	27,064	401
Commercial [Member] | Energy [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	10
Commercial [Member] | Energy [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	86,489	0
Commercial [Member] | Healthcare [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	3,316,556	3,027,329
Nonaccrual	3,645	4,480
Total	3,325,790	3,033,916
Past Due 90 Days or More and Accruing	171
Commercial [Member] | Healthcare [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	5,419	2,039
Commercial [Member] | Healthcare [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
Commercial [Member] | Healthcare [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	3,815	68
Commercial [Member] | Services [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	3,521,644	3,105,621
Nonaccrual	25,817	7,483
Total	3,545,825	3,122,163
Past Due 90 Days or More and Accruing	58
Commercial [Member] | Services [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	6,503	1,737
Commercial [Member] | Services [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	5,168	523
Commercial [Member] | Services [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	12,510	6,799
Commercial [Member] | Wholesale/retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		1,758,878
Nonaccrual		1,163
Total		1,760,866
Commercial [Member] | Wholesale/retail [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		712
Commercial [Member] | Wholesale/retail [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		113
Commercial [Member] | Wholesale/retail [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial [Member] | General business [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	2,955,752
Nonaccrual	13,675
Total	2,976,990
Past Due 90 Days or More and Accruing	443
Commercial [Member] | General business [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	14,002
Commercial [Member] | General business [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	342
Commercial [Member] | General business [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	6,894
Commercial [Member] | Manufacturing [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		654,329
Nonaccrual		10,133
Total		665,449
Commercial [Member] | Manufacturing [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		410
Commercial [Member] | Manufacturing [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		190
Commercial [Member] | Manufacturing [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		387
Commercial [Member] | Public finance [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		707,638
Nonaccrual		0
Total		709,868
Commercial [Member] | Public finance [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		2,230
Commercial [Member] | Public finance [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial [Member] | Public finance [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial [Member] | Other commercial and industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		764,390
Nonaccrual		435
Total		766,011
Commercial [Member] | Other commercial and industrial [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		414
Commercial [Member] | Other commercial and industrial [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		772
Commercial [Member] | Other commercial and industrial [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	4,673,416	4,400,576
Nonaccrual	12,952	27,626
Total	4,693,700	4,433,783
Past Due 90 Days or More and Accruing	4,771
Commercial real estate [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	2,029	4,920
Commercial real estate [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	532	250
Commercial real estate [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	17,723	411
Commercial real estate [Member] | Residential construction and land development [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		147,379
Nonaccrual		350
Total		150,879
Commercial real estate [Member] | Residential construction and land development [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		3,093
Commercial real estate [Member] | Residential construction and land development [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Residential construction and land development [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		57
Commercial real estate [Member] | Retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		756,653
Nonaccrual		18,868
Total		775,521
Commercial real estate [Member] | Retail [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Retail [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Retail [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Office [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		928,379
Nonaccrual		0
Total		928,379
Commercial real estate [Member] | Office [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Office [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Office [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Multifamily [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		1,258,704
Nonaccrual		6,858
Total		1,265,562
Commercial real estate [Member] | Multifamily [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Multifamily [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Multifamily [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		855,208
Nonaccrual		909
Total		856,117
Commercial real estate [Member] | Industrial [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Industrial [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Industrial [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Commercial real estate [Member] | Other commercial real estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		454,253
Nonaccrual		641
Total		457,325
Commercial real estate [Member] | Other commercial real estate [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		1,827
Commercial real estate [Member] | Other commercial real estate [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		250
Commercial real estate [Member] | Other commercial real estate [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		354
Paycheck Protection Program
Financing receivable, recorded investment, aging [Abstract]
Current	2,097,325
Total	2,097,325
Past Due 90 Days or More and Accruing	0
Paycheck Protection Program | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0
Paycheck Protection Program | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0
Paycheck Protection Program | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0
Loans to individuals [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	3,215,171	1,895,939
Nonaccrual	38,248	37,622
Total	3,446,569	2,084,172
Past Due 90 Days or More and Accruing	119,429
Loans to individuals [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	64,662	29,557
Loans to individuals [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	36,003	18,648
Loans to individuals [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	130,733	102,406
Loans to individuals [Member] | Residential mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	1,830,005
Nonaccrual	31,599
Total	1,849,144	2,084,172
Past Due 90 Days or More and Accruing	2,241
Loans to individuals [Member] | Residential mortgage [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	8,299
Loans to individuals [Member] | Residential mortgage [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	1,128
Loans to individuals [Member] | Residential mortgage [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	9,712
Loans to individuals [Member] | Residential mortgage [Member] | US Government Agency Insured Loans [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	172,678
Nonaccrual	6,397
Total	384,247
Past Due 90 Days or More and Accruing	117,188
Loans to individuals [Member] | Residential mortgage [Member] | US Government Agency Insured Loans [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	56,264
Loans to individuals [Member] | Residential mortgage [Member] | US Government Agency Insured Loans [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	34,355
Loans to individuals [Member] | Residential mortgage [Member] | US Government Agency Insured Loans [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	120,950
Loans to individuals [Member] | Permanent Residential Mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		1,034,716
Nonaccrual		20,441
Total		1,057,321
Loans to individuals [Member] | Permanent Residential Mortgage [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		2,011
Loans to individuals [Member] | Permanent Residential Mortgage [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		153
Loans to individuals [Member] | Permanent Residential Mortgage [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Loans to individuals [Member] | Permanent Residential Mortgage [Member] | US Government Agency Insured Loans [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		46,898
Nonaccrual		6,100
Total		197,794
Loans to individuals [Member] | Permanent Residential Mortgage [Member] | US Government Agency Insured Loans [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		24,203
Loans to individuals [Member] | Permanent Residential Mortgage [Member] | US Government Agency Insured Loans [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		18,187
Loans to individuals [Member] | Permanent Residential Mortgage [Member] | US Government Agency Insured Loans [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		102,406
Loans to individuals [Member] | Home equity [Member]
Financing receivable, recorded investment, aging [Abstract]
Current		814,325
Nonaccrual		11,081
Total		829,057
Loans to individuals [Member] | Home equity [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		3,343
Loans to individuals [Member] | Home equity [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		308
Loans to individuals [Member] | Home equity [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due		0
Loans to individuals [Member] | Personal [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	1,212,488	1,196,362
Nonaccrual	252	287
Total	1,213,178	1,201,382
Past Due 90 Days or More and Accruing	0
Loans to individuals [Member] | Personal [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	99	4,664
Loans to individuals [Member] | Personal [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	520	54
Loans to individuals [Member] | Personal [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	$ 71	$ 15