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Summary of Significant Accounting Policies - Narrative (Details) | 12 Months Ended
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Dec. 31, 2023 USD ($) segment subsidiary | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($)
Property, Plant and Equipment |  |  |
Deficiency (benefit) of stock-based compensation plans | $ 300,000 | $ 200,000 | $ (500,000)
Impairment losses | $ 0 | 0 | 0
Number of significant subsidiaries | subsidiary | 1 |  |
Income tax examination, penalties | $ 0 | 0 | 0
Cash on deposit with Federal Reserve Bank | 199,000,000 | 518,900,000 |
Federal Reserve Bank stock | 94,200,000 | 93,600,000 |
Federal Home Loan Bank stock | 127,800,000 | 103,800,000 |
Advertising expense | 900,000 | 3,800,000 | $ 2,600,000
Loans and Leases Receivable Disclosure [Line Items] |  |  |
Accrued interest receivable | 129,100,000 | 118,300,000 |
Accrued Investment Income Receivable | 38,500,000 | 38,900,000 |
Hosting Arrangement, Service Contract, Implementation Cost, Expense, Amortization | $ 2,300,000 | 3,400,000 |
Number of operating segments | segment | 1 |  |
Total investment securities | $ 1,200,000 | 1,200,000 |
Buildings and improvements | Minimum |  |  |
Property, Plant and Equipment |  |  |
Estimated useful lives | 5 years |  |
Buildings and improvements | Maximum [Member] |  |  |
Property, Plant and Equipment |  |  |
Estimated useful lives | 45 years |  |
Furniture and equipment | Minimum |  |  |
Property, Plant and Equipment |  |  |
Estimated useful lives | 3 years |  |
Furniture and equipment | Maximum [Member] |  |  |
Property, Plant and Equipment |  |  |
Estimated useful lives | 15 years |  |
Loans |  |  |
Loans and Leases Receivable Disclosure [Line Items] |  |  |
Accrued interest receivable | $ 86,100,000 | $ 76,500,000 |

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- Definition Amount of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to expense for award under share-based payment arrangement. Excludes expense determined to be nondeductible upon grant or after for award under share-based payment arrangement. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 12 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482685/740-10-50-12 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Name Accounting Standards Codification -Section 35 -Paragraph 2 -SubTopic 740 -Topic 718 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480887/718-740-35-2 + Details
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