Fair Value (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Estimated fair value	$ 402,905,000	$ 245,249,000
Mutual funds held in deferred compensation trust
Mutual funds held in deferred compensation trust	1,514,000	1,320,000
Mortgage-Backed Securities
Estimated fair value	223,305,000	145,314,000
U.S. Government Sponsored Enterprises [Member]
Estimated fair value	14,677,000	7,507,000
State and Political Subdivisions
Estimated fair value	156,933,000	92,428,000
Level 1 | Mortgage-Backed Securities
Estimated fair value	0	0
Level 1 | U.S. Government Sponsored Enterprises [Member]
Estimated fair value	0	0
Level 1 | State and Political Subdivisions
Estimated fair value	0	0
Level 2 | State and Political Subdivisions
Estimated fair value	156,933,000	92,428,000
Level 2 | Mortgage-Backed Securities
Estimated fair value	223,305,000	145,314,000
Level 2 | U.S. Government Sponsored Enterprises
Estimated fair value	14,677,000	7,507,000
Level 3 | Mortgage-Backed Securities
Estimated fair value	0	0
Level 3 | U.S. Treasuries
Estimated fair value	0
Level 3 | State and Political Subdivisions
Estimated fair value	0	0
Level 3 | U.S. Government Sponsored Enterprises
Estimated fair value	0	0
Level 1
Estimated fair value	0	0
Level 1 | Mutual funds held in deferred compensation trust
Mutual funds held in deferred compensation trust	0	0
Level 2
Estimated fair value	402,905,000	245,249,000
Level 2 | Mutual funds held in deferred compensation trust
Mutual funds held in deferred compensation trust	1,514,000	1,320,000
Level 3
Estimated fair value	0	0
Level 3 | Mutual funds held in deferred compensation trust
Mutual funds held in deferred compensation trust	0	$ 0
U.S. Treasuries [Member] | Level 1
Estimated fair value	0
U.S. Treasuries [Member] | Level 2
Estimated fair value	7,990,000
U.S. Treasuries [Member]
Estimated fair value	$ 7,990,000