Concentrations of risk and geographic information - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenue, Major Customer [Line Items]
Revenue	$ 280,507,000	$ 131,169,000	$ 534,153,000	$ 666,306,000
Document Period End Date			Sep. 30, 2020
United States [Member]
Revenue, Major Customer [Line Items]
Revenue	141,000,000.0	$ 50,900,000	$ 263,500,000	$ 251,600,000
Outside the United States [Member]
Revenue, Major Customer [Line Items]
Long-lived assets	$ 8,400,000		$ 8,400,000		$ 11,000,000.0