Loans and Allowance for Credit Losses for Loans - Amortized Cost In Those Loan Classes Based on Payment Activity 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
90 Days or More Past Due Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	5,718	13,541
Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	687,724	730,764
Year two, fiscal year before current fiscal year	703,682	781,246
Year three, two years before current fiscal year	673,655	688,973
Year four, three years before current fiscal year	521,589	586,114
Year five, four years before current fiscal year	450,274	384,867
More than five years before current fiscal year	1,122,039	946,981
Revolving Loans Amortized Cost Basis	68,012	64,798
Revolving Loans Converted to Term Loans	0	0
Total	4,226,975	4,183,743
Residential mortgage | 90 Days or More Past Due Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	956	3,170
Residential mortgage | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	687,724	730,764
Year two, fiscal year before current fiscal year	701,963	778,161
Year three, two years before current fiscal year	671,803	684,761
Year four, three years before current fiscal year	519,568	582,650
Year five, four years before current fiscal year	446,367	380,723
More than five years before current fiscal year	1,108,317	943,616
Revolving Loans Amortized Cost Basis	68,012	64,798
Revolving Loans Converted to Term Loans	0	0
Total	4,203,754	4,165,473
Residential mortgage | Non-Performing Loans | 90 Days or More Past Due Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	0	0
Year two, fiscal year before current fiscal year	1,719	3,085
Year three, two years before current fiscal year	1,852	4,212
Year four, three years before current fiscal year	2,021	3,464
Year five, four years before current fiscal year	3,907	4,144
More than five years before current fiscal year	13,722	3,365
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans	0	0
Total	23,221	18,270
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	460,358	446,991
Year two, fiscal year before current fiscal year	390,977	454,481
Year three, two years before current fiscal year	370,704	290,819
Year four, three years before current fiscal year	227,353	161,744
Year five, four years before current fiscal year	116,266	57,330
More than five years before current fiscal year	56,279	37,456
Revolving Loans Amortized Cost Basis	1,212,315	1,200,000
Revolving Loans Converted to Term Loans	46,792	52,017
Total	2,881,044	2,700,838
Consumer loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	7,120	8,580
Year two, fiscal year before current fiscal year	7,314	10,634
Year three, two years before current fiscal year	8,925	11,756
Year four, three years before current fiscal year	9,332	8,886
Year five, four years before current fiscal year	6,946	5,365
More than five years before current fiscal year	15,566	15,476
Revolving Loans Amortized Cost Basis	308,861	319,247
Revolving Loans Converted to Term Loans	46,792	51,609
Total	410,856	431,553
Consumer loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	447,285	426,140
Year two, fiscal year before current fiscal year	376,562	438,289
Year three, two years before current fiscal year	355,153	272,248
Year four, three years before current fiscal year	211,171	151,746
Year five, four years before current fiscal year	108,283	50,888
More than five years before current fiscal year	32,808	16,644
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans	0	0
Total	1,531,262	1,355,955
Consumer loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	5,953	12,271
Year two, fiscal year before current fiscal year	7,101	5,558
Year three, two years before current fiscal year	6,626	6,815
Year four, three years before current fiscal year	6,850	1,112
Year five, four years before current fiscal year	1,037	1,077
More than five years before current fiscal year	7,905	5,336
Revolving Loans Amortized Cost Basis	903,454	880,753
Revolving Loans Converted to Term Loans	0	408
Total	938,926	913,330
Consumer loans | 90 Days or More Past Due Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	463	271
Consumer loans | 90 Days or More Past Due Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total	0	0
Consumer loans | 90 Days or More Past Due Loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total	441	245
Consumer loans | 90 Days or More Past Due Loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total	22	26
Consumer loans | Performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	7,120	8,580
Year two, fiscal year before current fiscal year	7,314	10,634
Year three, two years before current fiscal year	8,925	11,756
Year four, three years before current fiscal year	9,332	8,886
Year five, four years before current fiscal year	6,946	5,340
More than five years before current fiscal year	15,485	15,393
Revolving Loans Amortized Cost Basis	307,985	318,869
Revolving Loans Converted to Term Loans	46,238	50,879
Total	409,345	430,337
Consumer loans | Performing | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	447,260	426,121
Year two, fiscal year before current fiscal year	376,473	438,181
Year three, two years before current fiscal year	354,978	272,075
Year four, three years before current fiscal year	210,941	151,523
Year five, four years before current fiscal year	108,085	50,853
More than five years before current fiscal year	32,683	16,550
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans	0	0
Total	1,530,420	1,355,303
Consumer loans | Performing | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	5,953	12,271
Year two, fiscal year before current fiscal year	7,101	5,558
Year three, two years before current fiscal year	6,626	6,815
Year four, three years before current fiscal year	6,850	1,112
Year five, four years before current fiscal year	1,037	1,077
More than five years before current fiscal year	7,905	5,314
Revolving Loans Amortized Cost Basis	903,454	880,748
Revolving Loans Converted to Term Loans	0	0
Total	938,926	912,895
Consumer loans | Non-Performing Loans | 90 Days or More Past Due Loans | Home equity
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	25
More than five years before current fiscal year	81	83
Revolving Loans Amortized Cost Basis	876	378
Revolving Loans Converted to Term Loans	554	730
Total	1,511	1,216
Consumer loans | Non-Performing Loans | 90 Days or More Past Due Loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	25	19
Year two, fiscal year before current fiscal year	89	108
Year three, two years before current fiscal year	175	173
Year four, three years before current fiscal year	230	223
Year five, four years before current fiscal year	198	35
More than five years before current fiscal year	125	94
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans	0	0
Total	842	652
Consumer loans | Non-Performing Loans | 90 Days or More Past Due Loans | Other consumer
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	0	22
Revolving Loans Amortized Cost Basis	0	5
Revolving Loans Converted to Term Loans	0	408
Total	$ 0	$ 435