Investment Securities - Amortized cost and estimated fair value (Details) $ in Thousands	Mar. 31, 2022 USD ($)
Carrying Value
Due within one year or less	$ 7,452
Due after one year through five years	35,474
Due after five years through ten years	73,557
Due after 10 years	223,667
Total investment securities	340,150
Estimated Fair Value
Due within one year or less	7,423
Due after one year through five years	33,923
Due after five years through ten years	69,032
Due after 10 years	207,448
Total investment securities	317,826
Amortized Cost
Due within one year or less	1
Due after one year through five years	8,456
Due after five years through ten years	100,021
Due after 10 years	815,189
Total investment securities available-for-sale	923,667
Fair Value
Due within one year or less	1
Due after one year through five years	8,316
Due after five years through ten years	98,740
Due after 10 years	759,276
Total investment securities available-for-sale	$ 866,333