Securities - Amortized cost and fair value by contractual maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Amortized Cost
Due after one year through five years	$ 101,073
Due after five years through ten years	382,261
Due after ten years	2,153,339
Total	2,636,673	$ 2,683,241
Fair Value
Due after one year through five years	94,058
Due after five years through ten years	337,412
Due after ten years	1,796,142
Fair Value	2,227,612	2,250,168
Amortized Cost
Due in one year or less	254,326
Due after one year through five years	309,053
Due after five years through ten years	1,148,155
Due after ten years	4,264,967
Amortized Cost	5,976,501	6,216,141
Fair Value
Due in one year or less	250,191
Due after one year through five years	295,225
Due after five years through ten years	1,001,653
Due after ten years	3,612,930
Fair Value	$ 5,159,999	$ 5,326,822