Stockholders' equity - Preferred stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	2 Months Ended	12 Months Ended
	Feb. 24, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stockholders Equity Note [Line Items]
Preferred stock shares authorized		30,000,000	30,000,000
Preferred stock shares outstanding		885,726	885,726	885,726	2,006,391
Preferred Stock | 2003 Series A Preferred Stock
Stockholders Equity Note [Line Items]
Preferred Stock Redemption Price Per Share		$ 25.00
Preferred stock liquidation preference		25
Preferred stock dividends per share cash paid		$ 0.1328125
Preferred stock dividend rate percentage		6.375%
Dividend preferred stock cash paid		$ 1.4	$ 1.4	$ 1.4
Preferred Stock | 2008 Series B Preferred Stock
Stockholders Equity Note [Line Items]
Preferred Stock Redemption Price Per Share	$ 25.00
Accrued and unpaid dividends on each share	0.1375
Dividends perferred stock per share	$ 25.1375