Stockholders' equity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 29, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Oct. 31, 2019
Preferred stock
Preferred stock redemption charge		$ 0	$ 0	$ (2,580)
Conversion of 7.00% Series D preferred stock (in shares)					578,000
Shares of common stock authorized		200,000,000
Shares of common stock issued and outstanding		158,043,880	136,690,329
Shares of preferred stock authorized		100,000,000
Shares of preferred stock issued and outstanding		0
Number of "excess stock" authorized (in shares)		200,000,000
Number of excess stock authorized issued and outstanding (in shares)		0
Series D Convertible Preferred Stock
Preferred stock
Preferred Stock, Shares Outstanding		0	0	0
Number of shares converted/redeemed	2,300,000			275,000
Aggregate price on repurchase of Series D preferred stock				$ 9,200
Aggregate price on repurchase of Series D preferred stock, per share				$ 33.60
Preferred stock redemption charge				$ (2,600)
Write off of Stock Issuance Costs				$ 215
Conversion rate (in shares)			0.2513
Closing sales price per share that the then-applicable conversion price must exceed in order for the shares to be automatically converted				$ 149.46