Fair value measurements - Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Fair value measurements on a recurring basis
Available-for-sale investment securities	$ 1,061,687	$ 1,136,439
Fair value measurements on a recurring basis | Quoted prices in active markets for identical assets (Level 1)
Derivative assets
Derivative assets	5	0
Derivative liabilities
Derivative liabilities	0	18
Fair value measurements on a recurring basis | Quoted prices in active markets for identical assets (Level 1) | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis | Quoted prices in active markets for identical assets (Level 1) | Bank | Interest rate lock commitments
Derivative assets
Derivative assets	0	0
Fair value measurements on a recurring basis | Quoted prices in active markets for identical assets (Level 1) | Bank | Forward commitments
Derivative assets
Derivative assets	5	0
Derivative liabilities
Derivative liabilities	0	18
Fair value measurements on a recurring basis | Quoted prices in active markets for identical assets (Level 1) | Interest rate swap (Other segment) | Interest rate swap
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative liabilities	0	0
Fair value measurements on a recurring basis | Quoted prices in active markets for identical assets (Level 1) | Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis | Quoted prices in active markets for identical assets (Level 1) | U.S. Treasury and federal agency obligations | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis | Quoted prices in active markets for identical assets (Level 1) | Corporate bonds | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis | Quoted prices in active markets for identical assets (Level 1) | Mortgage revenue bonds | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis | Significant  other observable  inputs (Level 2)
Derivative assets
Derivative assets	1,817	1,058
Derivative liabilities
Derivative liabilities	0	303
Fair value measurements on a recurring basis | Significant  other observable  inputs (Level 2) | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	1,047,611	1,122,081
Fair value measurements on a recurring basis | Significant  other observable  inputs (Level 2) | Bank | Interest rate lock commitments
Derivative assets
Derivative assets	89	86
Fair value measurements on a recurring basis | Significant  other observable  inputs (Level 2) | Bank | Forward commitments
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative liabilities	0	0
Fair value measurements on a recurring basis | Significant  other observable  inputs (Level 2) | Interest rate swap (Other segment) | Interest rate swap
Derivative assets
Derivative assets	1,728	972
Derivative liabilities
Derivative liabilities	0	303
Fair value measurements on a recurring basis | Significant  other observable  inputs (Level 2) | Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	1,005,801	1,077,168
Fair value measurements on a recurring basis | Significant  other observable  inputs (Level 2) | U.S. Treasury and federal agency obligations | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	8,883	12,010
Fair value measurements on a recurring basis | Significant  other observable  inputs (Level 2) | Corporate bonds | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	32,927	32,903
Fair value measurements on a recurring basis | Significant  other observable  inputs (Level 2) | Mortgage revenue bonds | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis | Significant unobservable inputs (Level 3)
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative liabilities	0	0
Fair value measurements on a recurring basis | Significant unobservable inputs (Level 3) | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	14,076	14,358
Fair value measurements on a recurring basis | Significant unobservable inputs (Level 3) | Bank | Interest rate lock commitments
Derivative assets
Derivative assets	0	0
Fair value measurements on a recurring basis | Significant unobservable inputs (Level 3) | Bank | Forward commitments
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative liabilities	0	0
Fair value measurements on a recurring basis | Significant unobservable inputs (Level 3) | Interest rate swap (Other segment) | Interest rate swap
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative liabilities	0	0
Fair value measurements on a recurring basis | Significant unobservable inputs (Level 3) | Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis | Significant unobservable inputs (Level 3) | U.S. Treasury and federal agency obligations | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis | Significant unobservable inputs (Level 3) | Corporate bonds | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis | Significant unobservable inputs (Level 3) | Mortgage revenue bonds | Bank
Fair value measurements on a recurring basis
Available-for-sale investment securities	$ 14,076	$ 14,358