Notes Receivable and Allowance for Losses - Schedule of notes receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	$ 139,317	$ 133,014
Total allowance for notes receivable credit losses	19,484	4,556	$ 4,685
Total notes receivable, net of allowance	119,833	128,458
Current portion, net of allowance	24,048	25,404
Long-term portion, net of allowance	95,785	103,054
Senior
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	104,716	98,545
Subordinated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	33,234	32,153
Unsecured
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	$ 1,367	$ 2,316