Transfers of financial assets and servicing assets - Initial fair value of assets obtained as proceeds from residential mortgage loans securitized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	$ 305,597	$ 743,847
Level 1
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0
Level 2
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	300,279	732,533
Level 3
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	5,318	11,314
Trading account debt securities
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	300,279	732,533
Trading account debt securities | Level 1
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0
Trading account debt securities | Level 2
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	300,279	732,533
Trading account debt securities | Level 3
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0
Trading account debt securities | GNMA
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	169,352	380,228
Trading account debt securities | GNMA | Level 1
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0
Trading account debt securities | GNMA | Level 2
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	169,352	380,228
Trading account debt securities | GNMA | Level 3
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0
Trading account debt securities | FNMA
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	122,422	329,617
Trading account debt securities | FNMA | Level 1
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0
Trading account debt securities | FNMA | Level 2
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	122,422	329,617
Trading account debt securities | FNMA | Level 3
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0
Trading account debt securities | FHLMC
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	8,505	22,688
Trading account debt securities | FHLMC | Level 1
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0
Trading account debt securities | FHLMC | Level 2
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	8,505	22,688
Trading account debt securities | FHLMC | Level 3
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0
Mortgage Servicing Rights
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	5,318	11,314
Mortgage Servicing Rights | Level 1
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0
Mortgage Servicing Rights | Level 2
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	0	0
Mortgage Servicing Rights | Level 3
Assets
Initial fair value of the assets obtained as proceeds from residential mortgage loans securitized	$ 5,318	$ 11,314