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Summary of Significant Accounting Policies (Details) |  |  | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Jan. 01, 2020 USD ($) | Oct. 01, 2019 USD ($) | Jun. 30, 2018 USD ($) | Dec. 31, 2020 USD ($) item | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Jan. 01, 2019 USD ($)
Number of insurance-related subsidiaries | item |  |  |  | 1 |  |  |
Investment Securities |  |  |  |  |  |  |
Number of components in which other-than-temporary impairment is segregated | item |  |  |  | 2 |  |  |
Non-Accrual Loans |  |  |  |  |  |  |
Period of charge off for past due unsecured consumer loans |  |  |  | 90 days |  |  |
Minimum period that past due unsecured loans outstanding may not be placed on nonaccrual status under special circumstances |  |  |  | 90 days |  |  |
Maximum period of non-consumer loans outstanding that is used to evaluate whether loans should be placed on non-accrual status |  |  |  | 90 days |  |  |
Other Real Estate Owned and Repossessed Assets |  |  |  |  |  |  |
Other real estate owned |  |  |  | $ 60,487,300 | $ 71,103,000 |  |
Repossessed assets |  |  |  |  | 7,137,000 |  |
Income Taxes |  |  |  |  |  |  |
Percentage of likelihood of realization of recognized tax benefit |  |  |  | 50.00% |  |  |
Liability for unrecognized tax benefits |  |  |  | $ 0 | 0 |  |
Interest expense related to uncertain tax positions |  |  |  | 0 | 0 | $ 0 |
Penalties related to uncertain tax positions |  |  |  | 0 | 0 | $ 0 |
Goodwill and Identified Intangible Assets |  |  |  |  |  |  |
Goodwill impairment loss |  | $ 0 |  |  |  |  |
Impairment of identified intangible assets |  |  |  | $ 0 |  |  |
Segments of an Enterprise and Related Information |  |  |  |  |  |  |
Number of operating segments | item |  |  |  | 1 |  |  |
Number of active operating bank subsidiaries | item |  |  |  | 5 |  |  |
New Accounting Standards |  |  |  |  |  |  |
One-time reclassification from AOCI to retained earnings, relating to the Tax Cuts and Jobs Act of 2017 |  |  | $ 5,997,000 |  |  |  |
Right-of-use asset amortization |  |  |  | $ 1,357,000 | 1,019,000 |  |
Retained Earnings (Accumulated Deficit) |  |  |  | $ 2,289,626,000 | $ 2,200,568,000 |  |
ASU 2016-02 |  |  |  |  |  |  |
New Accounting Standards |  |  |  |  |  |  |
Right of use asset, statement of Financial Position Location |  |  |  |  |  |  | us-gaap:OtherAssets
Lease liability, statement of Financial Position Location |  |  |  |  |  |  | us-gaap:OtherLiabilities
ASU 2016-02 | Adjusted Balance |  |  |  |  |  |  |
New Accounting Standards |  |  |  |  |  |  |
Right of use asset |  |  |  |  |  |  | $ 6,400,000
Lease liability |  |  |  |  |  |  | $ 6,400,000
ASU 2016-13 | Adjustment |  |  |  |  |  |  |
New Accounting Standards |  |  |  |  |  |  |
Percentage of Increase in Allowance for Loan Losses | 17.20% |  |  |  |  |  |
Retained Earnings (Accumulated Deficit) | $ 8,300,000 |  |  |  |  |  |

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