Notes Receivable and Allowance for Credit Losses - Credit Quality Indicator (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Notes Receivable and Allowance for Losses [Line Items]
2020	$ 0
2019	25,840
2018	32,667
Prior	81,515
Total	140,022	$ 133,014
Senior
Notes Receivable and Allowance for Losses [Line Items]
2020	0
2019	23,570
2018	20,546
Prior	60,808
Total	104,924	98,545
Subordinated
Notes Receivable and Allowance for Losses [Line Items]
2020	0
2019	2,270
2018	11,492
Prior	18,881
Total	32,643	32,153
Unsecured
Notes Receivable and Allowance for Losses [Line Items]
2020	0
2019	0
2018	629
Prior	1,826
Total	$ 2,455	$ 2,316