Receivables and Allowance for Credit Losses - Past Due Balances Of Mezzanine And Other Notes Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Notes receivable	$ 159,128	$ 139,317
Senior Notes
Financing Receivable, Past Due [Line Items]
Notes receivable	123,526	104,716
Subordinated
Financing Receivable, Past Due [Line Items]
Notes receivable	34,192	33,234
Unsecured
Financing Receivable, Past Due [Line Items]
Notes receivable	1,410	1,367
1- 30 days Past Due
Financing Receivable, Past Due [Line Items]
Notes receivable	0	0
1- 30 days Past Due | Senior Notes
Financing Receivable, Past Due [Line Items]
Notes receivable	0	0
1- 30 days Past Due | Subordinated
Financing Receivable, Past Due [Line Items]
Notes receivable	0	0
1- 30 days Past Due | Unsecured
Financing Receivable, Past Due [Line Items]
Notes receivable	0	0
31-89 days Past Due
Financing Receivable, Past Due [Line Items]
Notes receivable	0	0
31-89 days Past Due | Senior Notes
Financing Receivable, Past Due [Line Items]
Notes receivable	0	0
31-89 days Past Due | Subordinated
Financing Receivable, Past Due [Line Items]
Notes receivable	0	0
31-89 days Past Due | Unsecured
Financing Receivable, Past Due [Line Items]
Notes receivable	0	0
> 90 days Past Due
Financing Receivable, Past Due [Line Items]
Notes receivable	26,755	17,409
> 90 days Past Due | Senior Notes
Financing Receivable, Past Due [Line Items]
Notes receivable	17,917	15,200
> 90 days Past Due | Subordinated
Financing Receivable, Past Due [Line Items]
Notes receivable	8,838	2,209
> 90 days Past Due | Unsecured
Financing Receivable, Past Due [Line Items]
Notes receivable	0	0
Total Past Due
Financing Receivable, Past Due [Line Items]
Notes receivable	26,755	17,409
Total Past Due | Senior Notes
Financing Receivable, Past Due [Line Items]
Notes receivable	17,917	15,200
Total Past Due | Subordinated
Financing Receivable, Past Due [Line Items]
Notes receivable	8,838	2,209
Total Past Due | Unsecured
Financing Receivable, Past Due [Line Items]
Notes receivable	0	0
Current
Financing Receivable, Past Due [Line Items]
Notes receivable	132,373	121,908
Current | Senior Notes
Financing Receivable, Past Due [Line Items]
Notes receivable	105,609	89,516
Current | Subordinated
Financing Receivable, Past Due [Line Items]
Notes receivable	25,354	31,025
Current | Unsecured
Financing Receivable, Past Due [Line Items]
Notes receivable	$ 1,410	$ 1,367