Servicing rights - Estimated valuation (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
SBA servicing rights | Minimum
Servicing rights, valuation assumptions
Forward prepayment assumptions	1.50%	0.00%
Forward default rate	0.00%	0.00%
Discount rate	11.60%	14.40%
Servicing expense (as a percent)	0.40%	0.40%
SBA servicing rights | Maximum
Servicing rights, valuation assumptions
Forward prepayment assumptions	21.60%	4.50%
Forward default rate	6.60%	7.30%
Discount rate	20.90%	22.90%
Servicing expense (as a percent)	0.40%	0.40%
SBA servicing rights | Weighted Average
Servicing rights, valuation assumptions
Forward prepayment assumptions	9.10%	4.40%
Forward default rate	6.30%	7.00%
Discount rate	12.20%	14.60%
Servicing expense (as a percent)	0.40%	0.40%
Multi-family servicing rights | Minimum
Servicing rights, valuation assumptions
Forward prepayment assumptions	0.00%	0.00%
Forward default rate	0.00%	0.00%
Discount rate	6.00%	6.00%
Servicing expense (as a percent)	0.00%	0.00%
Multi-family servicing rights | Maximum
Servicing rights, valuation assumptions
Forward prepayment assumptions	6.50%	6.50%
Forward default rate	0.90%	0.90%
Discount rate	6.00%	6.00%
Servicing expense (as a percent)	0.80%	0.80%
Multi-family servicing rights | Weighted Average
Servicing rights, valuation assumptions
Forward prepayment assumptions	5.60%	5.40%
Forward default rate	0.60%	0.60%
Discount rate	6.00%	6.00%
Servicing expense (as a percent)	0.10%	0.10%
USDA | Minimum
Servicing rights, valuation assumptions
Forward prepayment assumptions	2.10%
Discount rate	6.90%
Servicing expense (as a percent)	0.30%
USDA | Maximum
Servicing rights, valuation assumptions
Forward prepayment assumptions	6.50%
Discount rate	6.90%
Servicing expense (as a percent)	0.30%
USDA | Weighted Average
Servicing rights, valuation assumptions
Forward prepayment assumptions	5.60%
Discount rate	6.90%
Servicing expense (as a percent)	0.30%