Stockholders' equity - Narrative (Details)	Jun. 01, 2020 $ / shares shares	Sep. 30, 2020 $ / shares shares	May 31, 2020 shares	Dec. 31, 2019 $ / shares shares
Equity [Abstract]
Conversation ratio of reverse stock split	0.05
Common stock authorized (shares)	22,500,000	22,500,000	450,000,000	22,500,000
Common stock par value (USD per share) | $ / shares	$ 0.01	$ 0.01		$ 0.01
Preferred stock authorized (shares)	50,000,000	50,000,000		50,000,000
Preferred stock par value (USD per share) | $ / shares	$ 0.01	$ 0.01		$ 0.01
Capital stock authorized (shares)	72,500,000