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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Earnings Per Share, Basic and Diluted [Abstract]
Net income	$ 211,421	$ 218,079	$ 423,107	$ 480,711
Preferred stock dividends	(353)	(353)	(706)	(706)
Net income applicable to common stock	$ 211,068	$ 217,726	$ 422,401	$ 480,005
Average common shares outstanding	76,171,784	81,609,435	77,301,469	82,748,275
Average potential dilutive common shares	115,099	163,354	124,805	140,103
Average common shares outstanding - assuming dilution	76,286,883	81,772,789	77,426,274	82,888,378
Basic EPS	$ 2.77	$ 2.67	$ 5.46	$ 5.80
Diluted EPS	$ 2.77	$ 2.66	$ 5.46	$ 5.79