Loans and Allowances for Credit Losses, By Aging Category (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing receivable, recorded investment, aging [Abstract]
Current	$ 23,721,124	$ 21,392,306
Nonaccrual	255,396	180,951
Total	24,155,890	21,750,987
Past Due 90 Days or More and Accruing	232,193	7,680
30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	81,221	47,084
60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	32,875	20,560
90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	320,670	110,086
Commercial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	14,020,368	13,899,429
Nonaccrual	201,999	115,416
Total	14,158,510	14,031,650
Past Due 90 Days or More and Accruing	10,465
Commercial [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	50,247	7,943
Commercial [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	9,675	1,608
Commercial [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	78,220	7,254
Commercial [Member] | Energy [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	3,893,481	3,881,244
Nonaccrual	162,989	91,722
Total	3,974,174	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	32,439	401
Commercial [Member] | Energy [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	3,889	10
Commercial [Member] | Energy [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	44,365	0
Commercial [Member] | Healthcare [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	3,284,305	3,027,329
Nonaccrual	3,645	4,480
Total	3,289,343	3,033,916
Past Due 90 Days or More and Accruing	0
Commercial [Member] | Healthcare [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	1,216	2,039
Commercial [Member] | Healthcare [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	177	0
Commercial [Member] | Healthcare [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	3,645	68
Commercial [Member] | Services [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	3,754,841	3,105,621
Nonaccrual	21,032	7,483
Total	3,779,881	3,122,163
Past Due 90 Days or More and Accruing	632
Commercial [Member] | Services [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	7,357	1,737
Commercial [Member] | Services [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	4,440	523
Commercial [Member] | Services [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	13,243	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	3,087,741
Nonaccrual	14,333
Total	3,115,112
Past Due 90 Days or More and Accruing	9,833
Commercial [Member] | General business [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	9,235
Commercial [Member] | General business [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	1,169
Commercial [Member] | General business [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	16,967
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	4,536,541	4,400,576
Nonaccrual	13,956	27,626
Total	4,554,144	4,433,783
Past Due 90 Days or More and Accruing	469
Commercial real estate [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	2,749	4,920
Commercial real estate [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	5,874	250
Commercial real estate [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	8,980	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	2,081,428
Total	2,081,428
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	3,082,787	1,895,939
Nonaccrual	39,441	37,622
Total	3,361,808	2,084,172
Past Due 90 Days or More and Accruing	221,259
Loans to individuals [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	28,225	29,557
Loans to individuals [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	17,326	18,648
Loans to individuals [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	233,470	102,406
Loans to individuals [Member] | Residential mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	1,797,197
Nonaccrual	33,098
Total	1,813,442	2,084,172
Past Due 90 Days or More and Accruing	42
Loans to individuals [Member] | Residential mortgage [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	7,254
Loans to individuals [Member] | Residential mortgage [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	1,360
Loans to individuals [Member] | Residential mortgage [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	7,631
Loans to individuals [Member] | Residential mortgage [Member] | US Government Agency Insured Loans [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	60,121
Nonaccrual	6,110
Total	322,269
Past Due 90 Days or More and Accruing	221,201
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	20,494
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	15,908
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	225,746
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	1,225,469	1,196,362
Nonaccrual	233	287
Total	1,226,097	1,201,382
Past Due 90 Days or More and Accruing	16
Loans to individuals [Member] | Personal [Member] | 30 to 59 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	477	4,664
Loans to individuals [Member] | Personal [Member] | 60 to 89 Days [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	58	54
Loans to individuals [Member] | Personal [Member] | 90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	$ 93	$ 15