Investment Securities - Amortized cost and fair value by contractual maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Amortized Cost
Due after one year through five years	$ 64,365
Due after five years through ten years	414,499
Due after ten years	2,327,601
Total	2,806,465	$ 1,819,901
Fair Value
Due after one year through five years	63,287
Due after five years through ten years	388,263
Due after ten years	2,041,136
Fair Value	2,492,686	1,778,064
Amortized Cost
Due in one year or less	58,779
Due after one year through five years	539,288
Due after five years through ten years	1,110,003
Due after ten years	4,609,053
Amortized Cost	6,317,123	5,221,296
Fair Value
Due in one year or less	58,123
Due after one year through five years	529,936
Due after five years through ten years	1,008,452
Due after ten years	4,069,497
Fair Value	$ 5,666,008	$ 5,193,478