Supplemental equity information - Preferred Stock (Details) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Class of Stock
Preferred stock authorized (in shares)	300,000	300,000
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, outstanding (in shares)	0	0
Preferred stock, issued (in shares)	0	0
Series A Junior Participating Preferred Stock
Class of Stock
Preferred stock authorized (in shares)	150,000	150,000
Preferred stock, outstanding (in shares)	0