Securities - Amortized Cost and Fair Value by Maturity Date (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized cost
Within one year	$ 653
After one to five years	7,462
After five to ten years	63,547
After ten years	544,101
Total	615,763	$ 717,682
Estimated fair value
Within one year	654
After one to five years	7,631
After five to ten years	68,932
After ten years	572,684
Total	$ 649,901	739,473
Weighted average yield
Within one year	8.02%
After one to five years	5.44%
After five to ten years	3.52%
After ten years	2.59%
Total	2.73%
Mortgage-backed - GSE residential
Amortized cost
Within one year	$ 0
After one to five years	55
After five to ten years	199
After ten years	121,839
Total	122,093	151,037
Estimated fair value
Within one year	0
After one to five years	58
After five to ten years	213
After ten years	126,512
Total	$ 126,783	152,512
Weighted average yield
Within one year	0.00%
After one to five years	4.57%
After five to ten years	3.91%
After ten years	2.03%
Total	2.06%
Collateralized mortgage obligations - GSE residential
Amortized cost
Within one year	$ 0
After one to five years	0
After five to ten years	2,496
After ten years	69,239
Total	71,735	128,876
Estimated fair value
Within one year	0
After one to five years	0
After five to ten years	2,735
After ten years	70,264
Total	$ 72,999	129,212
Weighted average yield
Within one year	0.00%
After one to five years	0.00%
After five to ten years	2.77%
After ten years	1.10%
Total	1.16%
State and political subdivisions
Amortized cost
Within one year	$ 653
After one to five years	7,407
After five to ten years	59,992
After ten years	353,023
Total	421,075	436,448
Estimated fair value
Within one year	654
After one to five years	7,573
After five to ten years	65,059
After ten years	375,908
Total	$ 449,194	456,340
Weighted average yield
Within one year	8.02%
After one to five years	5.44%
After five to ten years	3.52%
After ten years	3.08%
Total	3.19%
Corporate bonds
Amortized cost
Within one year	$ 0
After one to five years	0
After five to ten years	860
After ten years	0
Total	860	1,321
Estimated fair value
Within one year	0
After one to five years	0
After five to ten years	925
After ten years	0
Total	$ 925	$ 1,409
Weighted average yield
Within one year	0.00%
After one to five years	0.00%
After five to ten years	5.57%
After ten years	0.00%
Total	5.57%