Marketplace Revenue - Disaggregation of Revenue by Source (Details) - Transferred over Time - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 46,907	$ 212,651	$ 604,234
Transaction fees
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	32,673	207,640	598,760
Referral fees
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 14,234	$ 5,011	$ 5,474