Fair value measurements - Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Fair value measurements on a recurring basis
Available-for-sale investment securities	$ 1,368,037	$ 1,429,667
Fair value measurements on a recurring basis | Quoted prices in active markets for identical assets (Level 1)
Derivative assets
Derivative assets	51	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	51	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	1,291	1,330
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	1,353,407	1,414,765
Fair value measurements on a recurring basis | Significant  other observable  inputs (Level 2) | Bank | Interest rate lock commitments
Derivative assets
Derivative assets	88	9
Fair value measurements on a recurring basis | Significant  other observable  inputs (Level 2) | Bank | Forward commitments
Derivative assets
Derivative assets	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	1,203	1,321
Derivative liabilities
Derivative liabilities	540	472
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	1,234,514	1,292,968
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	77,747	81,063
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	41,146	40,734
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
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	14,630	14,902
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
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	$ 14,630	$ 14,902