Basis of Presentation and Summary of Significant Accounting Policies - Summary of Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Contract assets:
Beginning balance	$ 1,484	$ 1,666
Additions	11,850	13,624
Deductions	(9,855)	(13,806)
Ending balance	3,479	1,484
Contract liabilities:
Beginning balance	1,474	1,175
Additions	3,761	5,348
Deductions	(3,911)	(5,049)
Ending balance	$ 1,324	$ 1,474