Investments - Carrying value and estimated fair value (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Mar. 31, 2026	Dec. 31, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024
Available-for-Sale Securities
Amortized  Cost	$ 605,273		$ 509,083
Gross Unrealized Gains	212		208
Gross Unrealized Losses	(35,397)		(39,881)
Estimated Fair Value	570,088		469,410
Allowance for Credit Losses	0		0
Held-to-Maturity Securities
Amortized  Cost	276,414		287,557
Gross Unrealized Gains	198		114
Gross Unrealized Losses	(20,540)		(20,022)
Estimated Fair Value	256,072		267,649
Allowance for Credit Losses	353	$ 407	440	$ 786	$ 974	$ 1,156
U.S. Treasury securities
Available-for-Sale Securities
Amortized  Cost	9,996		9,996
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(502)		(487)
Estimated Fair Value	9,494		9,509
Allowance for Credit Losses	0		0
U.S. Government agencies
Available-for-Sale Securities
Amortized  Cost	2,491		66
Gross Unrealized Gains	1		0
Gross Unrealized Losses	(5)		(3)
Estimated Fair Value	2,487		63
Allowance for Credit Losses	0		0
Obligations of states and political subdivisions
Available-for-Sale Securities
Amortized  Cost	183,976		180,395
Gross Unrealized Gains	1		5
Gross Unrealized Losses	(13,204)		(14,439)
Estimated Fair Value	170,773		165,961
Allowance for Credit Losses	0		0
Held-to-Maturity Securities
Amortized  Cost	192,406		192,308
Gross Unrealized Gains	36		55
Gross Unrealized Losses	(13,832)		(13,595)
Estimated Fair Value	178,610		178,768
Allowance for Credit Losses	20		20
U.S. Government sponsored entities and agencies collateralized by residential mortgage obligations
Available-for-Sale Securities
Amortized  Cost	225,797		67,588
Gross Unrealized Gains	16		94
Gross Unrealized Losses	(4,506)		(2,985)
Estimated Fair Value	221,307		64,697
Allowance for Credit Losses	0		0
Held-to-Maturity Securities
Amortized  Cost	11,622		11,443
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(1,748)		(1,632)
Estimated Fair Value	9,874		9,811
Allowance for Credit Losses	0		0
Private label mortgage and asset backed securities
Available-for-Sale Securities
Amortized  Cost	166,817		250,575
Gross Unrealized Gains	57		61
Gross Unrealized Losses	(17,175)		(21,967)
Estimated Fair Value	149,699		228,669
Allowance for Credit Losses	0		0
Held-to-Maturity Securities
Amortized  Cost	45,749		51,397
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(3,796)		(3,282)
Estimated Fair Value	41,953		48,115
Allowance for Credit Losses	31		25
Corporate debt securities
Available-for-Sale Securities
Amortized  Cost	16,196		463
Gross Unrealized Gains	137		48
Gross Unrealized Losses	(5)		0
Estimated Fair Value	16,328		511
Allowance for Credit Losses	0
Held-to-Maturity Securities
Amortized  Cost	26,637		32,409
Gross Unrealized Gains	162		59
Gross Unrealized Losses	(1,164)		(1,513)
Estimated Fair Value	25,635		30,955
Allowance for Credit Losses	$ 302		$ 395