Net income per common share - Computation of net income (loss) per common share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Earnings Per Share
Net income	$ 155,323	$ 136,609	$ 436,395	$ 446,748
Preferred stock dividends	(353)	(353)	(1,059)	(1,059)
Net income applicable to common stock	$ 154,970	$ 136,256	$ 435,336	$ 445,689
Average common shares outstanding	71,807,136	71,794,934	71,882,273	71,676,630
Average potential dilutive common shares	21,266	23,168	29,880	59,884
Average common shares outstanding - assuming dilution	71,828,402	71,818,102	71,912,153	71,736,514
Basic EPS	$ 2.16	$ 1.90	$ 6.06	$ 6.22
Diluted EPS	$ 2.16	$ 1.90	$ 6.05	$ 6.21