Investment Securities - Amortized cost and estimated fair value (Details) $ in Thousands	Sep. 30, 2021 USD ($)
Carrying Value
Due within one year or less	$ 4,690
Due after one year through five years	34,282
Due after five years through ten years	75,197
Due after 10 years	248,417
Total investment securities	362,586
Estimated Fair Value
Due within one year or less	4,690
Due after one year through five years	34,359
Due after five years through ten years	76,120
Due after 10 years	248,371
Total investment securities	363,540
Amortized Cost
Due after one year through five years	3,270
Due after five years through ten years	83,891
Due after 10 years	568,399
Total investment securities available-for-sale	655,560
Fair Value
Due after one year through five years	3,376
Due after five years through ten years	87,330
Due after 10 years	564,576
Total investment securities available-for-sale	$ 655,282