Supplemental equity information - Rights Agreement (Details) - USD ($) $ in Millions	Apr. 06, 2020	Dec. 31, 2019
Equity [Abstract]
Operating loss carryforwards		$ 435
Rights agreement, dividend declared (in shares)	1
Rights agreement, percent of common stock owned required for exercise	4.99%
Rights agreement, additional percent of common stock owned required for exercise	0.50%
Exercise percent discount	50.00%
Number of shares that may be exchanged per right (in shares)	1