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	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 50,311,702		$ 50,311,702		$ 50,210,295
Gross loan charge-offs
Total	38,339	$ 11,327	63,239	$ 43,900
Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,800,000		1,800,000
90 Days or More Past Due Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	14,478		14,478		13,145
Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	210,754		210,754		467,178
Year two, fiscal year before current fiscal year	450,310		450,310		1,305,994
Year three, two years before current fiscal year	1,298,181		1,298,181		1,506,814
Year four, three years before current fiscal year	1,479,529		1,479,529		540,210
Year five, four years before current fiscal year	514,213		514,213		439,060
More than five years before current fiscal year	1,594,237		1,594,237		1,250,931
Revolving Loans Amortized Cost Basis	78,117		78,117		57,052
Revolving Loans Converted to Term Loans	1,772		1,772		1,771
Total	5,627,113		5,627,113		5,569,010
Gross loan charge-offs
Total	0	149	0	149
Residential mortgage | 90 Days or More Past Due Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	2,609		2,609		2,488
Residential mortgage | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	210,754		210,754		467,178
Year two, fiscal year before current fiscal year	450,310		450,310		1,304,026
Year three, two years before current fiscal year	1,295,317		1,295,317		1,505,133
Year four, three years before current fiscal year	1,478,365		1,478,365		538,853
Year five, four years before current fiscal year	513,072		513,072		435,669
More than five years before current fiscal year	1,583,270		1,583,270		1,244,986
Revolving Loans Amortized Cost Basis	78,117		78,117		57,052
Revolving Loans Converted to Term Loans	1,772		1,772		1,771
Total	5,610,977		5,610,977		5,554,668
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		0
Year two, fiscal year before current fiscal year	0		0		1,968
Year three, two years before current fiscal year	2,864		2,864		1,681
Year four, three years before current fiscal year	1,164		1,164		1,357
Year five, four years before current fiscal year	1,141		1,141		3,391
More than five years before current fiscal year	10,967		10,967		5,945
Revolving Loans Amortized Cost Basis	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	16,136		16,136		14,342
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	463,966		463,966		541,513
Year two, fiscal year before current fiscal year	479,132		479,132		597,411
Year three, two years before current fiscal year	508,623		508,623		374,145
Year four, three years before current fiscal year	293,606		293,606		127,568
Year five, four years before current fiscal year	93,764		93,764		101,615
More than five years before current fiscal year	199,945		199,945		135,506
Revolving Loans Amortized Cost Basis	1,352,145		1,352,145		1,538,050
Revolving Loans Converted to Term Loans	45,415		45,415		24,887
Total	3,436,596		3,436,596		3,440,695
Gross loan charge-offs
Total	1,262	$ 1,040	3,071	$ 1,868
Consumer loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	9,088		9,088		40,599
Year two, fiscal year before current fiscal year	33,421		33,421		44,944
Year three, two years before current fiscal year	41,756		41,756		14,961
Year four, three years before current fiscal year	10,908		10,908		4,096
Year five, four years before current fiscal year	3,690		3,690		4,850
More than five years before current fiscal year	53,149		53,149		47,406
Revolving Loans Amortized Cost Basis	403,918		403,918		396,960
Revolving Loans Converted to Term Loans	10,537		10,537		5,336
Total	566,467		566,467		559,152
Consumer loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	442,959		442,959		468,242
Year two, fiscal year before current fiscal year	416,986		416,986		532,012
Year three, two years before current fiscal year	448,522		448,522		356,198
Year four, three years before current fiscal year	280,436		280,436		121,750
Year five, four years before current fiscal year	88,921		88,921		86,384
More than five years before current fiscal year	85,028		85,028		34,813
Revolving Loans Amortized Cost Basis	0		0		20,227
Revolving Loans Converted to Term Loans	0		0		763
Total	1,762,852		1,762,852		1,620,389
Consumer loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	11,919		11,919		32,672
Year two, fiscal year before current fiscal year	28,725		28,725		20,455
Year three, two years before current fiscal year	18,345		18,345		2,986
Year four, three years before current fiscal year	2,262		2,262		1,722
Year five, four years before current fiscal year	1,153		1,153		10,381
More than five years before current fiscal year	61,768		61,768		53,287
Revolving Loans Amortized Cost Basis	948,227		948,227		1,120,863
Revolving Loans Converted to Term Loans	34,878		34,878		18,788
Total	1,107,277		1,107,277		1,261,154
Consumer loans | 90 Days or More Past Due Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	898		898		1,088
Consumer loans | 90 Days or More Past Due Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total	0		0		0
Consumer loans | 90 Days or More Past Due Loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total	606		606		576
Consumer loans | 90 Days or More Past Due Loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total	292		292		512
Consumer loans | Performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	9,088		9,088		40,599
Year two, fiscal year before current fiscal year	33,421		33,421		44,893
Year three, two years before current fiscal year	41,705		41,705		14,948
Year four, three years before current fiscal year	10,895		10,895		4,096
Year five, four years before current fiscal year	3,690		3,690		4,850
More than five years before current fiscal year	52,290		52,290		46,274
Revolving Loans Amortized Cost Basis	403,918		403,918		396,960
Revolving Loans Converted to Term Loans	10,492		10,492		4,608
Total	565,499		565,499		557,228
Consumer loans | Performing | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	442,959		442,959		468,152
Year two, fiscal year before current fiscal year	416,685		416,685		531,728
Year three, two years before current fiscal year	448,353		448,353		356,144
Year four, three years before current fiscal year	280,337		280,337		121,658
Year five, four years before current fiscal year	88,898		88,898		86,147
More than five years before current fiscal year	84,848		84,848		34,504
Revolving Loans Amortized Cost Basis	0		0		20,227
Revolving Loans Converted to Term Loans	0		0		763
Total	1,762,080		1,762,080		1,619,323
Consumer loans | Performing | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, current fiscal year	11,919		11,919		32,662
Year two, fiscal year before current fiscal year	28,714		28,714		20,376
Year three, two years before current fiscal year	18,284		18,284		2,986
Year four, three years before current fiscal year	2,262		2,262		1,722
Year five, four years before current fiscal year	1,153		1,153		10,381
More than five years before current fiscal year	61,730		61,730		52,659
Revolving Loans Amortized Cost Basis	948,227		948,227		1,120,863
Revolving Loans Converted to Term Loans	34,875		34,875		18,655
Total	1,107,164		1,107,164		1,260,304
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		0
Year two, fiscal year before current fiscal year	0		0		51
Year three, two years before current fiscal year	51		51		13
Year four, three years before current fiscal year	13		13		0
Year five, four years before current fiscal year	0		0		0
More than five years before current fiscal year	859		859		1,132
Revolving Loans Amortized Cost Basis	0		0		0
Revolving Loans Converted to Term Loans	45		45		728
Total	968		968		1,924
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	0		0		90
Year two, fiscal year before current fiscal year	301		301		284
Year three, two years before current fiscal year	169		169		54
Year four, three years before current fiscal year	99		99		92
Year five, four years before current fiscal year	23		23		237
More than five years before current fiscal year	180		180		309
Revolving Loans Amortized Cost Basis	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	772		772		1,066
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		10
Year two, fiscal year before current fiscal year	11		11		79
Year three, two years before current fiscal year	61		61		0
Year four, three years before current fiscal year	0		0		0
Year five, four years before current fiscal year	0		0		0
More than five years before current fiscal year	38		38		628
Revolving Loans Amortized Cost Basis	0		0		0
Revolving Loans Converted to Term Loans	3		3		133
Total	$ 113		113		850
Gross loan charge-offs
Gross loan charge-offs
Year one, gross loan charge-offs			45		296
Year two, gross loan charge-offs			638		903
Year three, gross loan charge-offs			968		357
Year four, gross loan charge-offs			430		232
Year five, gross loan charge-offs			347		752
More than five years gross loan charge-offs			615		1,921
Revolving Loans Amortized Cost Basis			0		31
Revolving Loans Converted to Term Loans			28		0
Total			$ 3,071		$ 4,492