Loans and Allowance for Credit Losses for Loans - Internal Loan Classification Risk by Loan Portfolio Class by Origination Year (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 32,686,416	$ 32,217,112
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	1,093,423	3,064,630
Year two, fiscal year before current fiscal year	2,455,868	624,427
Year three, two years before current fiscal year	576,690	570,901
Year four, three years before current fiscal year	532,223	240,525
Year five, four years before current fiscal year	213,365	179,522
More than five years before current fiscal year	547,660	434,485
Revolving Loans Amortized Cost Basis	1,728,721	1,746,355
Revolving Loans Converted to Term Loans	694	863
Total	7,148,644	6,861,708
Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	1,091,421	3,058,596
Year two, fiscal year before current fiscal year	2,438,605	605,112
Year three, two years before current fiscal year	560,364	556,284
Year four, three years before current fiscal year	515,645	212,215
Year five, four years before current fiscal year	191,930	162,483
More than five years before current fiscal year	454,483	337,484
Revolving Loans Amortized Cost Basis	1,637,014	1,677,559
Revolving Loans Converted to Term Loans	296	350
Total	6,889,758	6,610,083
Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	1,027	819
Year two, fiscal year before current fiscal year	1,599	10,236
Year three, two years before current fiscal year	8,714	2,135
Year four, three years before current fiscal year	6,874	9,502
Year five, four years before current fiscal year	3,365	10,228
More than five years before current fiscal year	17,601	14,165
Revolving Loans Amortized Cost Basis	66,443	49,883
Revolving Loans Converted to Term Loans	37	51
Total	105,660	97,019
Commercial and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	975	5,215
Year two, fiscal year before current fiscal year	15,664	3,876
Year three, two years before current fiscal year	4,870	12,481
Year four, three years before current fiscal year	9,704	1,798
Year five, four years before current fiscal year	1,226	4,215
More than five years before current fiscal year	4,217	12,965
Revolving Loans Amortized Cost Basis	25,264	18,913
Revolving Loans Converted to Term Loans	361	462
Total	62,281	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	2,742	1
Year four, three years before current fiscal year	0	17,010
Year five, four years before current fiscal year	16,844	2,596
More than five years before current fiscal year	71,359	69,871
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans	0	0
Total	90,945	94,681
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total	18,709,958	18,470,823
Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	704,516	3,165,678
Year two, fiscal year before current fiscal year	3,180,133	3,137,328
Year three, two years before current fiscal year	3,093,175	2,305,380
Year four, three years before current fiscal year	2,230,995	1,875,959
Year five, four years before current fiscal year	1,812,028	1,876,523
More than five years before current fiscal year	5,689,256	4,145,217
Revolving Loans Amortized Cost Basis	198,835	203,381
Revolving Loans Converted to Term Loans	14,689	15,532
Total	16,923,627	16,724,998
Commercial real estate | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	703,940	3,096,549
Year two, fiscal year before current fiscal year	3,102,368	3,052,076
Year three, two years before current fiscal year	3,001,631	2,230,047
Year four, three years before current fiscal year	2,148,025	1,767,528
Year five, four years before current fiscal year	1,691,885	1,798,137
More than five years before current fiscal year	5,314,508	3,916,990
Revolving Loans Amortized Cost Basis	195,069	199,145
Revolving Loans Converted to Term Loans	14,597	15,532
Total	16,172,023	16,076,004
Commercial real estate | Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	0	50,193
Year two, fiscal year before current fiscal year	55,142	68,203
Year three, two years before current fiscal year	74,513	44,336
Year four, three years before current fiscal year	44,406	48,813
Year five, four years before current fiscal year	45,899	66,845
More than five years before current fiscal year	193,439	109,295
Revolving Loans Amortized Cost Basis	1,235	1,705
Revolving Loans Converted to Term Loans	0	0
Total	414,634	389,390
Commercial real estate | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	576	18,936
Year two, fiscal year before current fiscal year	22,623	17,049
Year three, two years before current fiscal year	17,031	30,997
Year four, three years before current fiscal year	38,564	59,618
Year five, four years before current fiscal year	74,244	11,541
More than five years before current fiscal year	181,107	118,725
Revolving Loans Amortized Cost Basis	2,531	2,531
Revolving Loans Converted to Term Loans	92	0
Total	336,768	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	202	207
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans	0	0
Total	202	207
Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	55,347	145,246
Year two, fiscal year before current fiscal year	154,851	121,869
Year three, two years before current fiscal year	100,871	111,420
Year four, three years before current fiscal year	106,812	18,125
Year five, four years before current fiscal year	15,422	57,984
More than five years before current fiscal year	67,064	37,823
Revolving Loans Amortized Cost Basis	1,285,964	1,253,358
Revolving Loans Converted to Term Loans	0	0
Total	1,786,331	1,745,825
Commercial real estate | Construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	55,347	145,246
Year two, fiscal year before current fiscal year	154,819	120,800
Year three, two years before current fiscal year	99,815	111,174
Year four, three years before current fiscal year	106,566	15,497
Year five, four years before current fiscal year	15,422	47,971
More than five years before current fiscal year	42,957	20,029
Revolving Loans Amortized Cost Basis	1,229,949	1,199,034
Revolving Loans Converted to Term Loans	0	0
Total	1,704,875	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	1,035	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	6,265	17,414
Revolving Loans Amortized Cost Basis	48,111	47,311
Revolving Loans Converted to Term Loans	0	0
Total	55,411	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	32	26
Year three, two years before current fiscal year	21	246
Year four, three years before current fiscal year	246	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	7,904	7,013
Revolving Loans Converted to Term Loans	0	0
Total	$ 26,045	$ 10,310