Loans and Allowance for Credit Losses for Loans - Internal Loan Classification Risk by Loan Portfolio Class by Origination Year (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 32,606,814	$ 32,217,112
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	1,532,789	3,064,630
Year two, fiscal year before current fiscal year	848,933	624,427
Year three, two years before current fiscal year	470,893	570,901
Year four, three years before current fiscal year	407,110	240,525
Year five, four years before current fiscal year	169,171	179,522
More than five years before current fiscal year	414,047	434,485
Revolving Loans Amortized Cost Basis	1,791,707	1,746,355
Revolving Loans Converted to Term Loans	610	863
Total	5,635,260	6,861,708
Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	1,526,393	3,058,596
Year two, fiscal year before current fiscal year	840,868	605,112
Year three, two years before current fiscal year	462,843	556,284
Year four, three years before current fiscal year	388,482	212,215
Year five, four years before current fiscal year	149,991	162,483
More than five years before current fiscal year	328,289	337,484
Revolving Loans Amortized Cost Basis	1,716,736	1,677,559
Revolving Loans Converted to Term Loans	269	350
Total	5,413,871	6,610,083
Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	1,809	819
Year two, fiscal year before current fiscal year	1,558	10,236
Year three, two years before current fiscal year	1,342	2,135
Year four, three years before current fiscal year	10,770	9,502
Year five, four years before current fiscal year	1,930	10,228
More than five years before current fiscal year	14,950	14,165
Revolving Loans Amortized Cost Basis	59,905	49,883
Revolving Loans Converted to Term Loans	53	51
Total	92,317	97,019
Commercial and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	4,587	5,215
Year two, fiscal year before current fiscal year	6,507	3,876
Year three, two years before current fiscal year	3,972	12,481
Year four, three years before current fiscal year	7,853	1,798
Year five, four years before current fiscal year	886	4,215
More than five years before current fiscal year	2,532	12,965
Revolving Loans Amortized Cost Basis	15,066	18,913
Revolving Loans Converted to Term Loans	288	462
Total	41,691	59,925
Commercial and industrial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	0	0
Year two, fiscal year before current fiscal year	0	5,203
Year three, two years before current fiscal year	2,736	1
Year four, three years before current fiscal year	5	17,010
Year five, four years before current fiscal year	16,364	2,596
More than five years before current fiscal year	68,276	69,871
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans	0	0
Total	87,381	94,681
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total	19,716,650	18,470,823
Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	3,180,913	3,165,678
Year two, fiscal year before current fiscal year	3,015,406	3,137,328
Year three, two years before current fiscal year	2,886,123	2,305,380
Year four, three years before current fiscal year	1,935,323	1,875,959
Year five, four years before current fiscal year	1,618,216	1,876,523
More than five years before current fiscal year	5,051,448	4,145,217
Revolving Loans Amortized Cost Basis	211,888	203,381
Revolving Loans Converted to Term Loans	12,753	15,532
Total	17,912,070	16,724,998
Commercial real estate | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	3,178,182	3,096,549
Year two, fiscal year before current fiscal year	2,936,284	3,052,076
Year three, two years before current fiscal year	2,801,710	2,230,047
Year four, three years before current fiscal year	1,851,162	1,767,528
Year five, four years before current fiscal year	1,498,151	1,798,137
More than five years before current fiscal year	4,716,223	3,916,990
Revolving Loans Amortized Cost Basis	170,763	199,145
Revolving Loans Converted to Term Loans	12,753	15,532
Total	17,165,228	16,076,004
Commercial real estate | Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	1,988	50,193
Year two, fiscal year before current fiscal year	45,305	68,203
Year three, two years before current fiscal year	44,596	44,336
Year four, three years before current fiscal year	43,593	48,813
Year five, four years before current fiscal year	51,875	66,845
More than five years before current fiscal year	169,460	109,295
Revolving Loans Amortized Cost Basis	38,594	1,705
Revolving Loans Converted to Term Loans	0	0
Total	395,411	389,390
Commercial real estate | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	743	18,936
Year two, fiscal year before current fiscal year	33,817	17,049
Year three, two years before current fiscal year	39,817	30,997
Year four, three years before current fiscal year	40,568	59,618
Year five, four years before current fiscal year	68,190	11,541
More than five years before current fiscal year	165,574	118,725
Revolving Loans Amortized Cost Basis	2,531	2,531
Revolving Loans Converted to Term Loans	0	0
Total	351,240	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	191	207
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans	0	0
Total	191	207
Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	164,162	145,246
Year two, fiscal year before current fiscal year	109,866	121,869
Year three, two years before current fiscal year	63,361	111,420
Year four, three years before current fiscal year	66,227	18,125
Year five, four years before current fiscal year	6,181	57,984
More than five years before current fiscal year	46,340	37,823
Revolving Loans Amortized Cost Basis	1,348,443	1,253,358
Revolving Loans Converted to Term Loans	0	0
Total	1,804,580	1,745,825
Commercial real estate | Construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	160,031	145,246
Year two, fiscal year before current fiscal year	109,843	120,800
Year three, two years before current fiscal year	62,330	111,174
Year four, three years before current fiscal year	65,581	15,497
Year five, four years before current fiscal year	6,181	47,971
More than five years before current fiscal year	28,498	20,029
Revolving Loans Amortized Cost Basis	1,329,163	1,199,034
Revolving Loans Converted to Term Loans	0	0
Total	1,761,627	1,659,751
Commercial real estate | Construction | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	4,131	0
Year two, fiscal year before current fiscal year	0	1,043
Year three, two years before current fiscal year	1,018	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	0	17,414
Revolving Loans Amortized Cost Basis	9,497	47,311
Revolving Loans Converted to Term Loans	0	0
Total	14,646	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	23	26
Year three, two years before current fiscal year	13	246
Year four, three years before current fiscal year	646	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	9,783	7,013
Revolving Loans Converted to Term Loans	0	0
Total	$ 28,307	$ 10,310