Allowance for Doubtful Accounts - Notes Receivable Disaggregated by Vintage Year (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Current-period gross write-offs
2021	$ 0
2020	0
2019	0
2018	315
2017	2,494
Prior	0
Total	2,809	$ 0
Current-period recoveries
2021	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Total	0
Current-period net write-offs
2021	0
2020	0
2019	0
2018	315
2017	2,494
Prior	0
Total	2,809
Standard notes receivable
Financing Receivable, Credit Quality Indicator [Line Items]
2021	485
2020	11,466
2019	8,966
2018	19,117
2017	22,153
Prior	1,562
Total	63,749
Current-period gross write-offs
Total	9	0
Elevated risk notes receivable
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019	617
2018	0
2017	723
Prior	1,374
Total	2,714
Current-period gross write-offs
Total	$ 2,800	$ 0