Borrowings - Note Payable (Details) - USD ($)		3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 29, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Nov. 01, 2018	Feb. 01, 2018
During the period:
Total interest expense		$ 10,738,000	$ 17,525,000	$ 37,668,000	$ 53,559,000
Carrying value:
Notes payable		1,295,143,000		1,295,143,000		$ 1,294,070,000
Unused amount		2,957,954,000		2,957,954,000		908,320,000
Notes payable
Maximum loan amount		1,300,000,000		1,300,000,000
Cash pledged to creditors						52,599,000
Note Payable
During the period:
Average balance		$ 1,300,000,000	$ 1,300,000,000	$ 1,300,000,000	$ 1,300,000,000
Weighted-average interest rate (as a percent)		2.99%	5.11%	3.57%	5.21%
Total interest expense		$ 10,177,000	$ 17,044,000	$ 36,131,000	$ 52,118,000
Maximum daily amount outstanding		1,300,000,000	1,300,000,000	1,300,000,000	1,300,000,000
Carrying value:
Unpaid principal balance		1,300,000,000		1,300,000,000		1,300,000,000
Unamortized debt issuance costs		(4,857,000)		(4,857,000)		(5,930,000)
Notes payable		$ 1,295,143,000		$ 1,295,143,000		$ 1,294,070,000
Weighted-average interest rate (as a percent)		2.93%		2.93%		4.46%
Amortization of Financing Costs		$ 459,000	445,000	$ 1,400,000	1,300,000
Note Payable | Revolving credit agreement
Short-term debt
Maximum loan amount							$ 150,000,000
Carrying value:
Amortization of Financing Costs		561,000	$ 481,000	1,500,000	$ 1,400,000
Notes payable
Cash pledged to creditors						$ 52,600,000
Increase in loan amount				0		0
Note Payable | Credit Suisse AG
Short-term debt
Maximum loan amount								$ 600,000,000
Note Payable | Mortgage servicing rights
Carrying value:
Assets pledged to secure		2,213,344,000		2,213,344,000		2,861,442,000
Notes payable
Increase in loan amount				0		0
Note Payable | Servicing advances
Carrying value:
Assets pledged to secure		232,519,000		232,519,000		$ 207,460,000
Note Payable | Deposits
Carrying value:
Assets pledged to secure		192,597,000		$ 192,597,000
Notes Payable Term Loan 2018-GT1
Notes payable
Debt instrument option to extend period				2 years
Notes Payable Term Loan 2018-GT1 | LIBOR
Notes payable
Maximum loan amount		650,000,000		$ 650,000,000
Interest rate spread				2.85%
Notes Payable Term Loan 2018-GT2
Notes payable
Debt instrument option to extend period				2 years
Notes Payable Term Loan 2018-GT2 | LIBOR
Notes payable
Maximum loan amount		$ 650,000,000		$ 650,000,000
Interest rate spread				2.65%
Unsecured Senior Note
Notes payable
Maximum loan amount	$ 500,000,000
Stated interest rate (as a percent)	5.375%
Unsecured Senior Note | Before October 15, 2022
Notes payable
Redemption rate (as a percent)	100.00%
Unsecured Senior Note | Before October 15, 2022 with up to 40% principal redeemed
Notes payable
Redemption rate (as a percent)	105.375%
Unsecured Senior Note | Change of Control
Notes payable
Redemption rate (as a percent)	101.00%
Unsecured Senior Note | Maximum | Before October 15, 2022 with up to 40% principal redeemed
Notes payable
Aggregate principal amount of notes that can be redeemed	$ 40