Guarantees - Credit recourse - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Guarantee on loans sold or serviced with credit recourse
Guarantor Obligations
Valuation allowances and reserves balance	$ 12,651,000	$ 26,885,000	$ 12,651,000	$ 26,885,000	$ 15,662,000	$ 22,484,000	$ 31,305,000	$ 34,862,000
Serviced mortgage loans
Guarantor Obligations
Loans serviced	12,300,000,000		12,300,000,000			12,900,000,000
Loans with recourse
Guarantor Obligations
Loans serviced	800,000,000		800,000,000			$ 900,000,000
Loans with recourse | Serviced mortgage loans
Guarantor Obligations
Repurchased loans	2,000,000	131,000,000	17,000,000	143,000,000
Loans with recourse | Serviced mortgage loans | Bulk loan repurchase | Loans from FNMA and FHLMC
Guarantor Obligations
Repurchased loans		120,000,000
Credit recourse reserve		5,100,000
Securitization | Guarantee on loans sold or serviced with representation and warranties
Guarantor Obligations
Repurchased loans	$ 0	$ 0	$ 0	$ 0