Summary of significant accounting policies - Additional information (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Inventory	$ 14,900			$ 14,900			$ 6,600
Decrease to stockholders' equity	(416,551)		$ (403,881)	(416,551)	$ (403,881)		(379,640)
Other expense, net	(15,771)		(7,591)	(32,499)	(5,572)
Immaterial error related to classification of Indemnification from acquisition | Restatement adjustment
Business Acquisition [Line Items]
Long-term liabilities		$ 10,100
Other expense, net		300
Additional paid-in capital:
Business Acquisition [Line Items]
Decrease to stockholders' equity	$ (1,542,848)		$ (1,085,643)	$ (1,542,848)	$ (1,085,643)	$ (1,487,217)	(1,138,316)	$ (944,559)	$ (678,548)
Additional paid-in capital: | Immaterial error related to classification of Indemnification from acquisition | Restatement adjustment
Business Acquisition [Line Items]
Decrease to stockholders' equity		$ 10,400					$ 10,387