Revenue - Significant Changes in Contract Assets and Contract Liabilities Balances (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Contract assets:
Beginning balance	$ 11,253	$ 0
Transferred to receivables from contract assets recognized at the beginning of the period	(2,813)	0
Increase due to unbilled and recognized as revenue in excess of billings during the period, net of amounts transferred to receivables	5,021	8,439
Ending balance	13,461	8,439
Contract liabilities:
Beginning balance	22,055	19,164
Revenue recognized that was included in the contract liabilities beginning balance	(9,729)	(12,016)
Increase due to cash received and not recognized as revenue and billings in excess of revenue recognized during the period	7,989	20,611
Customer deposits reclassified to refund liabilities	0	(6,083)
Ending balance	$ 20,315	$ 21,676