Securities - Amortized cost and fair value by contractual maturity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Amortized Cost
Due in one year or less	$ 50,000
Due after one year through five years	50,955
Due after five years through ten years	480,806
Due after ten years	1,905,679
Total	2,487,440	$ 2,683,241
Fair Value
Due in one year or less	49,222
Due after one year through five years	46,440
Due after five years through ten years	414,831
Due after ten years	1,574,243
Fair Value	2,084,736	2,250,168
Amortized Cost
Due in one year or less	158,338
Due after one year through five years	267,073
Due after five years through ten years	1,343,076
Due after ten years	3,792,519
Amortized Cost	5,561,006	6,216,141
Fair Value
Due in one year or less	156,418
Due after one year through five years	254,908
Due after five years through ten years	1,165,142
Due after ten years	3,207,920
Fair Value	4,784,388	5,326,822
Information with respect to sales of held-to-maturity
Proceeds from sales of investment securities held to maturity	0	0	$ 0
Information with respect to sales of available-for-sale securities
Sale proceeds	129,614	482,028	151,314
Gross realized gains	1,335	103	750
Gross realized losses	1,292	73	648
Net realized gain	$ 43	$ 30	$ 102