Stockholders' equity - Narrative - Undesignated Preferred Stock and Common Stock (Details)	Jun. 30, 2019 vote $ / shares shares	Jun. 30, 2018 $ / shares shares
Share-based Payment Arrangement [Abstract]
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, shares authorized (in shares)	600,000,000	600,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001
Number of votes per share | vote	1