Stockholders' equity - Preferred stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
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	885,726
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 no par value	$ 0
Preferred stock shares outstanding	885,726	885,726	885,726