Revenues - Contract assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Contract with customer, liability	$ 0
Change in Contract with Customer, Asset [Roll Forward]
Contract asset at beginning of period	5,700,000	$ 6,200,000
Additions	21,500,000	23,600,000
Reclassification to accounts receivable, billed to customers	(21,900,000)	(24,100,000)
Contract asset at end of period	$ 5,300,000	$ 5,700,000