Fair value measurements - Fair Value Measurements on a Recurring Basis (Details) $ in Thousands	12 Months Ended
Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	$ 1,429,667	$ 2,574,618
Measurement Input, Discount Rate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Mortgage revenue bonds, measurement input	0.0489
Mortgage revenue bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, January 1	$ 15,427	27,185
Principal payments received	(525)	(11,758)
Purchases	0
Unrealized gain (loss) included in other comprehensive income	0	0
Balance, December 31	14,902	15,427
Fair value measurements on a recurring basis \| Level 1
Fair value measurements on a recurring and nonrecurring basis
Derivative assets	18	0
Derivative liabilities	0	11
Fair value measurements on a recurring basis \| Level 1 \| Bank
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis \| Level 1 \| Bank \| Interest rate lock commitments
Fair value measurements on a recurring and nonrecurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Fair value measurements on a recurring basis \| Level 1 \| Bank \| Forward commitments
Fair value measurements on a recurring and nonrecurring basis
Derivative assets	18	0
Derivative liabilities	0	11
Fair value measurements on a recurring basis \| Level 1 \| Bank \| Interest rate swap
Fair value measurements on a recurring and nonrecurring basis
Derivative assets	0	0
Fair value measurements on a recurring basis \| Level 1 \| Bank \| Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis \| Level 1 \| Bank \| U.S. Treasury and federal agency obligations
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis \| Level 1 \| Bank \| Corporate bonds
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis \| Level 1 \| Bank \| Mortgage revenue bonds
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis \| Level 1 \| Other \| Interest rate swap
Fair value measurements on a recurring and nonrecurring basis
Derivative liabilities	0	0
Fair value measurements on a recurring basis \| Level 2
Fair value measurements on a recurring and nonrecurring basis
Derivative assets	1,330	909
Derivative liabilities	472	5,271
Fair value measurements on a recurring basis \| Level 2 \| Bank
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	1,414,765	2,559,191
Fair value measurements on a recurring basis \| Level 2 \| Bank \| Interest rate lock commitments
Fair value measurements on a recurring and nonrecurring basis
Derivative assets	9	638
Derivative liabilities	0	0
Fair value measurements on a recurring basis \| Level 2 \| Bank \| Forward commitments
Fair value measurements on a recurring and nonrecurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Fair value measurements on a recurring basis \| Level 2 \| Bank \| Interest rate swap
Fair value measurements on a recurring and nonrecurring basis
Derivative assets	1,321	271
Fair value measurements on a recurring basis \| Level 2 \| Bank \| Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	1,292,968	2,437,923
Fair value measurements on a recurring basis \| Level 2 \| Bank \| U.S. Treasury and federal agency obligations
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	81,063	90,090
Fair value measurements on a recurring basis \| Level 2 \| Bank \| Corporate bonds
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	40,734	31,178
Fair value measurements on a recurring basis \| Level 2 \| Bank \| Mortgage revenue bonds
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis \| Level 2 \| Other \| Interest rate swap
Fair value measurements on a recurring and nonrecurring basis
Derivative liabilities	472	5,271
Fair value measurements on a recurring basis \| Level 3
Fair value measurements on a recurring and nonrecurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Fair value measurements on a recurring basis \| Level 3 \| Bank
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	14,902	15,427
Fair value measurements on a recurring basis \| Level 3 \| Bank \| Interest rate lock commitments
Fair value measurements on a recurring and nonrecurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Fair value measurements on a recurring basis \| Level 3 \| Bank \| Forward commitments
Fair value measurements on a recurring and nonrecurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Fair value measurements on a recurring basis \| Level 3 \| Bank \| Interest rate swap
Fair value measurements on a recurring and nonrecurring basis
Derivative assets	0	0
Fair value measurements on a recurring basis \| Level 3 \| Bank \| Mortgage-backed securities — issued or guaranteed by U.S. Government agencies or sponsored agencies
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis \| Level 3 \| Bank \| U.S. Treasury and federal agency obligations
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis \| Level 3 \| Bank \| Corporate bonds
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	0	0
Fair value measurements on a recurring basis \| Level 3 \| Bank \| Mortgage revenue bonds
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale investment securities	14,902	15,427
Fair value measurements on a recurring basis \| Level 3 \| Other \| Interest rate swap
Fair value measurements on a recurring and nonrecurring basis
Derivative liabilities	$ 0	$ 0

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
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Value of input used to measure 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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Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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