Net income per common share - Computation of net income (loss) per common share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Earnings Per Share
Net income	$ 614,212	$ 541,342	$ 1,102,641
Preferred stock dividends	(1,412)	(1,412)	(1,412)
Net income applicable to common stock	$ 612,800	$ 539,930	$ 1,101,229
Average common shares outstanding	71,590,757	71,710,265	75,147,263
Average potential dilutive common shares	32,945	81,427	126,740
Average common shares outstanding - assuming dilution	71,623,702	71,791,692	75,274,003
Basic EPS	$ 8.56	$ 7.53	$ 14.65
Diluted EPS	$ 8.56	$ 7.52	$ 14.63