Net income per common share - Computation of net income (loss) per common share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Earnings Per Share
Net income	$ 151,160	$ 211,421	$ 310,139	$ 423,107
Preferred stock dividends	(353)	(353)	(706)	(706)
Net income applicable to common stock	$ 150,807	$ 211,068	$ 309,433	$ 422,401
Average common shares outstanding	71,690,396	76,171,784	71,616,498	77,301,469
Average potential dilutive common shares	18,807	115,099	47,805	124,805
Average common shares outstanding - assuming dilution	71,709,203	76,286,883	71,664,303	77,426,274
Basic EPS	$ 2.10	$ 2.77	$ 4.32	$ 5.46
Diluted EPS	$ 2.10	$ 2.77	$ 4.32	$ 5.46