| Investing Receivables - Investing Receivables (Details) - Investing Receivables - USD ($) $ in Thousands | Sep. 30, 2023 | Dec. 31, 2022 | Sep. 30, 2022 | Dec. 31, 2021 | 
|---|---|---|---|---|
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||||
| Amortized cost basis | $ 91,158 | $ 87,415 | ||
| Allowance for credit losses | (3,623) | (2,794) | $ (3,728) | $ (1,599) | 
| Investing receivables, net | 87,535 | 84,621 | ||
| Notes receivable from the City of Huntsville | ||||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||||
| Amortized cost basis | 74,347 | 69,703 | ||
| Other investing loans receivable | ||||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||||
| Amortized cost basis | $ 16,811 | $ 17,712 | 
| X | ||||||||||
| 
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
 | 
| X | ||||||||||
| 
- Definition Amortized cost, before allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease. Reference 1: http://www.xbrl.org/2003/role/exampleRef 
 | 
| X | ||||||||||
| 
- Definition Amortized cost, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
 | 
| X | ||||||||||
| 
- Details 
 | 
| X | ||||||||||
| 
- Details 
 | 
| X | ||||||||||
| 
- Details 
 |