Notes Receivable and Allowance for Credit Losses - Credit Quality Indicator (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Notes Receivable and Allowance for Losses [Line Items]
2021	$ 0
2020	0
2019	31,572
Prior	108,983
Total	140,555	$ 139,317
Senior
Notes Receivable and Allowance for Losses [Line Items]
2021	0
2020	0
2019	28,981
Prior	76,352
Total	105,333	104,716
Subordinated
Notes Receivable and Allowance for Losses [Line Items]
2021	0
2020	0
2019	2,591
Prior	31,081
Total	33,672	33,234
Unsecured
Notes Receivable and Allowance for Losses [Line Items]
2021	0
2020	0
2019	0
Prior	1,550
Total	$ 1,550	$ 1,367