Notes Receivable and Allowance for Loan Losses - Changes in Allowance for Credit Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 0
Provision for unrealized credit losses	256	$ 0	$ 0
Financing Receivable, Allowance for Credit Loss, Extinguishment Due To Acquisition	(497)
Ending balance	2,584	0
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 2,825
Ending balance		$ 2,825