Stockholders' equity (Details) $ / shares in Units, $ in Millions			3 Months Ended
	May 28, 2019 item $ / shares	May 12, 2019	Mar. 31, 2019 USD ($)	Jun. 30, 2020 $ / shares shares	Dec. 31, 2019 $ / shares shares	Jan. 01, 2019 $ / shares
Stockholders' equity
Common stock, par value (in dollars per share) | $ / shares				$ 0.0001	$ 0.0001	$ 0.0001
Series A Junior Participating Preferred Stock
Stockholders' equity
Preferred stock, authorized shares | shares				2,400,000	2,400,000
Preferred stock, shares outstanding | shares				0	0
Rights offering
Stockholders' equity
Percentage of shares acquired by entity under tax plan		4.90%
Number of preferred stock purchase right granted as dividend | item	1
Number of additional shares of common stock upon exercise | item	1
Percentage of discount on additional shares of common stock upon exercise	50.00%
Rights offering | Series A Junior Participating Preferred Stock
Stockholders' equity
Percentage of right to purchase shares of preferred stock	0.01%
Share price | $ / shares	$ 30.92
Common Stock
Stockholders' equity
Reclassification of APIC due to U.S. Domestication | $			$ (1,713)
Additional paid in capital
Stockholders' equity
Reclassification of APIC due to U.S. Domestication | $			$ 1,713