Guarantees - Credit recourse - Additional Information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Guarantee on loans sold or serviced with credit recourse
Guarantor Obligations
Valuation allowances and reserves balance	$ 20,244,000	$ 31,719,000	$ 22,484,000	$ 34,862,000
Serviced Mortgage Loans
Guarantor Obligations
Loans serviced	12,700,000,000		12,900,000,000
Loans with Recourse
Guarantor Obligations
Loans serviced	900,000,000		900,000,000
Loans with Recourse | Serviced Mortgage Loans
Guarantor Obligations
Repurchased loans	8,000,000		$ 8,000,000
Securitization | Guarantee on loans sold or serviced with representation and warranties
Guarantor Obligations
Repurchased loans	$ 0	$ 0