Allowance for Doubtful Accounts - Allowance for doubtful accounts (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounts receivable
Accounts receivable, Allowance for doubtful accounts, beginning balance	$ 51,052	$ 39,903
Write-Offs	(7,305)	(4,409)
Bad Debt Expense	2,779	2,186
Accounts receivable, Allowance for doubtful accounts, ending balance	46,526	74,389
Notes receivable
Notes receivable, Allowance for doubtful accounts, beginning balance	14,576	17,891
Write-Offs	(2,809)	0
Bad Debt Expense	636	(126)
Notes receivable, Allowance for doubtful accounts, ending balance	16,749	12,490
Allowance for doubtful accounts, beginning balance	67,801	52,393
Write-Offs	(10,114)	(4,409)
Bad Debt Expense	3,415	2,060
Allowance for doubtful accounts, ending balance	61,102	92,280
Accounts receivable recovered after write off	0	0
Cumulative effect of ASC 326 adoption
Accounts receivable
Accounts receivable, Allowance for doubtful accounts, beginning balance		36,709
Notes receivable
Notes receivable, Allowance for doubtful accounts, ending balance		5,527
Allowance for doubtful accounts, beginning balance		42,236
Standard notes receivable
Notes receivable
Notes receivable, Allowance for doubtful accounts, beginning balance	12,993	11,654
Write-Offs	(9)	0
Bad Debt Expense	(256)	(249)
Notes receivable, Allowance for doubtful accounts, ending balance	13,258	6,667
Standard notes receivable | Cumulative effect of ASC 326 adoption
Notes receivable
Notes receivable, Allowance for doubtful accounts, ending balance		5,236
Elevated risk notes receivable
Notes receivable
Notes receivable, Allowance for doubtful accounts, beginning balance	1,583	6,237
Write-Offs	(2,800)	0
Bad Debt Expense	892	123
Notes receivable, Allowance for doubtful accounts, ending balance	$ 3,491	5,823
Elevated risk notes receivable | Cumulative effect of ASC 326 adoption
Notes receivable
Notes receivable, Allowance for doubtful accounts, ending balance		$ 291