Transfers of financial assets and servicing assets - Initial fair value of assets obtained as proceeds from residential mortgage loans securitized (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	$ 6,473	$ 11,900	$ 11,396	$ 36,903
Level 1
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0	0	0
Level 2
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	6,356	11,599	11,162	35,958
Level 3
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	117	301	234	945
Trading account debt securities
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	6,356	11,599	11,162	35,958
Trading account debt securities | Level 1
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0	0	0
Trading account debt securities | Level 2
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	6,356	11,599	11,162	35,958
Trading account debt securities | Level 3
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0	0	0
Trading account debt securities | GNMA
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	3,083	1,421	4,183	2,488
Trading account debt securities | GNMA | Level 1
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0	0	0
Trading account debt securities | GNMA | Level 2
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	3,083	1,421	4,183	2,488
Trading account debt securities | GNMA | Level 3
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0	0	0
Trading account debt securities | FNMA
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	3,273	10,178	6,979	33,470
Trading account debt securities | FNMA | Level 1
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0	0	0
Trading account debt securities | FNMA | Level 2
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	3,273	10,178	6,979	33,470
Trading account debt securities | FNMA | Level 3
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0	0	0
Mortgage Servicing Rights
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	117	301	234	945
Mortgage Servicing Rights | Level 1
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0	0	0
Mortgage Servicing Rights | Level 2
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0	0	0
Mortgage Servicing Rights | Level 3
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	$ 117	$ 301	$ 234	$ 945