Loans and Allowance for Credit Losses for Loans - Internal Loan Classification Risk by Loan Portfolio Class by Origination Year (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 32,457,454	$ 32,217,112
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	1,544,657	3,064,630
Year two, fiscal year before current fiscal year	1,237,686	624,427
Year three, two years before current fiscal year	516,809	570,901
Year four, three years before current fiscal year	458,231	240,525
Year five, four years before current fiscal year	181,507	179,522
More than five years before current fiscal year	496,511	434,485
Revolving Loans Amortized Cost Basis	1,648,444	1,746,355
Revolving Loans Converted to Term Loans	610	863
Total	6,084,455	6,861,708
Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	1,539,921	3,058,596
Year two, fiscal year before current fiscal year	1,227,478	605,112
Year three, two years before current fiscal year	508,228	556,284
Year four, three years before current fiscal year	438,246	212,215
Year five, four years before current fiscal year	162,119	162,483
More than five years before current fiscal year	409,413	337,484
Revolving Loans Amortized Cost Basis	1,571,927	1,677,559
Revolving Loans Converted to Term Loans	225	350
Total	5,857,557	6,610,083
Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	1,282	819
Year two, fiscal year before current fiscal year	1,550	10,236
Year three, two years before current fiscal year	1,476	2,135
Year four, three years before current fiscal year	11,182	9,502
Year five, four years before current fiscal year	2,159	10,228
More than five years before current fiscal year	17,041	14,165
Revolving Loans Amortized Cost Basis	59,376	49,883
Revolving Loans Converted to Term Loans	64	51
Total	94,130	97,019
Commercial and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	3,325	5,215
Year two, fiscal year before current fiscal year	8,658	3,876
Year three, two years before current fiscal year	4,366	12,481
Year four, three years before current fiscal year	8,803	1,798
Year five, four years before current fiscal year	859	4,215
More than five years before current fiscal year	1,374	12,965
Revolving Loans Amortized Cost Basis	17,141	18,913
Revolving Loans Converted to Term Loans	321	462
Total	44,847	59,925
Commercial and industrial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	129	0
Year two, fiscal year before current fiscal year	0	5,203
Year three, two years before current fiscal year	2,739	1
Year four, three years before current fiscal year	0	17,010
Year five, four years before current fiscal year	16,370	2,596
More than five years before current fiscal year	68,683	69,871
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans	0	0
Total	87,921	94,681
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total	19,264,980	18,470,823
Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	2,103,590	3,165,678
Year two, fiscal year before current fiscal year	3,129,360	3,137,328
Year three, two years before current fiscal year	2,967,080	2,305,380
Year four, three years before current fiscal year	2,088,996	1,875,959
Year five, four years before current fiscal year	1,668,795	1,876,523
More than five years before current fiscal year	5,326,049	4,145,217
Revolving Loans Amortized Cost Basis	215,423	203,381
Revolving Loans Converted to Term Loans	12,849	15,532
Total	17,512,142	16,724,998
Commercial real estate | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	2,100,741	3,096,549
Year two, fiscal year before current fiscal year	3,055,880	3,052,076
Year three, two years before current fiscal year	2,875,727	2,230,047
Year four, three years before current fiscal year	2,005,122	1,767,528
Year five, four years before current fiscal year	1,552,673	1,798,137
More than five years before current fiscal year	4,978,293	3,916,990
Revolving Loans Amortized Cost Basis	174,277	199,145
Revolving Loans Converted to Term Loans	12,849	15,532
Total	16,755,562	16,076,004
Commercial real estate | Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	2,000	50,193
Year two, fiscal year before current fiscal year	51,271	68,203
Year three, two years before current fiscal year	58,418	44,336
Year four, three years before current fiscal year	44,118	48,813
Year five, four years before current fiscal year	43,019	66,845
More than five years before current fiscal year	184,694	109,295
Revolving Loans Amortized Cost Basis	38,615	1,705
Revolving Loans Converted to Term Loans	0	0
Total	422,135	389,390
Commercial real estate | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	849	18,936
Year two, fiscal year before current fiscal year	22,209	17,049
Year three, two years before current fiscal year	32,935	30,997
Year four, three years before current fiscal year	39,756	59,618
Year five, four years before current fiscal year	73,103	11,541
More than five years before current fiscal year	162,866	118,725
Revolving Loans Amortized Cost Basis	2,531	2,531
Revolving Loans Converted to Term Loans	0	0
Total	334,249	259,397
Commercial real estate | Commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	0	0
Year two, fiscal year before current fiscal year	0	0
Year three, two years before current fiscal year	0	0
Year four, three years before current fiscal year	0	0
Year five, four years before current fiscal year	0	0
More than five years before current fiscal year	196	207
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans	0	0
Total	196	207
Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	112,491	145,246
Year two, fiscal year before current fiscal year	147,459	121,869
Year three, two years before current fiscal year	88,172	111,420
Year four, three years before current fiscal year	78,663	18,125
Year five, four years before current fiscal year	6,656	57,984
More than five years before current fiscal year	48,772	37,823
Revolving Loans Amortized Cost Basis	1,270,625	1,253,358
Revolving Loans Converted to Term Loans	0	0
Total	1,752,838	1,745,825
Commercial real estate | Construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	112,491	145,246
Year two, fiscal year before current fiscal year	147,431	120,800
Year three, two years before current fiscal year	87,130	111,174
Year four, three years before current fiscal year	78,332	15,497
Year five, four years before current fiscal year	6,656	47,971
More than five years before current fiscal year	29,216	20,029
Revolving Loans Amortized Cost Basis	1,251,972	1,199,034
Revolving Loans Converted to Term Loans	0	0
Total	1,713,228	1,659,751
Commercial real estate | Construction | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	0	0
Year two, fiscal year before current fiscal year	0	1,043
Year three, two years before current fiscal year	1,026	0
Year four, three years before current fiscal year	0	0
Year five, four years before current fiscal year	0	9,996
More than five years before current fiscal year	1,714	17,414
Revolving Loans Amortized Cost Basis	8,871	47,311
Revolving Loans Converted to Term Loans	0	0
Total	11,611	75,764
Commercial real estate | Construction | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	0	0
Year two, fiscal year before current fiscal year	28	26
Year three, two years before current fiscal year	16	246
Year four, three years before current fiscal year	331	2,628
Year five, four years before current fiscal year	0	17
More than five years before current fiscal year	17,842	380
Revolving Loans Amortized Cost Basis	9,782	7,013
Revolving Loans Converted to Term Loans	0	0
Total	$ 27,999	$ 10,310