Notes Receivable and Allowance for Credit Losses - Credit Quality Indicator (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Notes Receivable and Allowance for Losses [Line Items]
2020	$ 0
2019	28,211
2018	33,070
Prior	82,418
Total	143,699	$ 133,014
Senior
Notes Receivable and Allowance for Losses [Line Items]
2020	0
2019	25,847
2018	20,664
Prior	61,457
Total	107,968	98,545
Subordinated
Notes Receivable and Allowance for Losses [Line Items]
2020	0
2019	2,364
2018	11,785
Prior	19,135
Total	33,284	32,153
Unsecured
Notes Receivable and Allowance for Losses [Line Items]
2020	0
2019	0
2018	621
Prior	1,826
Total	$ 2,447	$ 2,316