Concentration of Third-party Mortgage Purchasers - Percent of Mortgage Loans Sold to Third-party Purchasers (Details) - Customer Concentration Risk - Mortgage Loans Sold	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
PennyMac Loan Services, LLC
Concentration Risk [Line Items]
Concentration risk percentage	33.00%	41.00%	23.00%
Fannie Mae
Concentration Risk [Line Items]
Concentration risk percentage	24.00%	7.00%	11.00%
Ginnie Mae
Concentration Risk [Line Items]
Concentration risk percentage	18.00%	4.00%	5.00%
Wells Fargo Funding, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	9.00%	16.00%	9.00%
U.S. Bancorp
Concentration Risk [Line Items]
Concentration risk percentage	3.00%	6.00%	11.00%
SunTrust Mortgage, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	0.00%	4.00%	11.00%
Flagstar Bancorp, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	0.00%	3.00%	11.00%