Income taxes (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 23,500,000	$ (3,700,000)	$ 19,900,000	$ 15,600,000
Pre-tax income (loss)	$ (80,500,000)	$ (11,300,000)	(212,600,000)	$ 120,300,000
Provision for income taxes related to BEAT			0		$ 0
Provision for income taxes related to GILTI			$ 0		$ 0