Revenue - Changes in contract assets and contract liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Contract assets
Transferred to receivables from contract assets recognized at the beginning of the period	$ (5,483)
Revenue recognized and not billed as of the end of the period	10,421
Net change in contract assets	4,938
Contract liabilities
Increases due to cash received, net of amounts recognized as revenue during the period	100,492
Contract liabilities assumed as part of acquisitions	2,350
Revenue recognized that was included in the contract liability balance as of the beginning of the period	(67,300)
Net change in contract liabilities	$ 35,542