Fair value measurements - Assets and liabilities measured on a recurring basis (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Fair value measurements on a recurring basis
Available-for-sale investment securities	$ 2,232,336	$ 2,574,618
Fair value measurements on a recurring basis \| Quoted prices in active markets for identical assets (Level 1)
Derivative liabilities
Derivative liabilities	0	11
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
Derivative assets
Derivative assets	172	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
Derivative liabilities
Derivative liabilities	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	172	0
Derivative liabilities
Derivative liabilities	0	11
Fair value measurements on a recurring basis \| Quoted prices in active markets for identical assets (Level 1) \| Other \| 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 liabilities
Derivative liabilities	88	5,271
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	2,217,303	2,559,191
Derivative assets
Derivative assets	2,077	909
Fair value measurements on a recurring basis \| Significant other observable inputs (Level 2) \| Bank \| Interest rate lock commitments
Derivative assets
Derivative assets	3	638
Derivative liabilities
Derivative liabilities	88	0
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) \| Other \| Interest rate swap
Derivative assets
Derivative assets	2,074	271
Derivative liabilities
Derivative liabilities	0	5,271
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	2,080,955	2,437,923
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	96,413	90,090
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	39,935	31,178
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 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	15,033	15,427
Derivative assets
Derivative assets	0	0
Fair value measurements on a recurring basis \| Significant unobservable inputs (Level 3) \| Bank \| Interest rate lock 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) \| 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) \| Other \| 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	$ 15,033	$ 15,427

Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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