Authorized shares of common and preferred stock and stock-based compensation plans - Schedule Of Weighted Average Grant Date Fair Value Of Purchase Rights Granted Under Employee Stock Purchase Plan (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of shares	909,274	872,853	1,065,154
Weighted average fair value per share (in dollars per share)	$ 9.40	$ 8.97	$ 6.80