Long-Term Debt - Note Payable (Details) - USD ($)		3 Months Ended		12 Months Ended
	Sep. 29, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Feb. 01, 2018
During the period:
Total interest expense		$ 9,888,000	$ 14,846,000
Unpaid principal balance		10,856,677,000
Unamortized debt issuance costs and premiums		(8,200,000)		$ (9,198,000)
Carrying value:
Notes payable		1,296,285,000		1,295,840,000
Notes payable
Maximum loan amount		1,300,000,000
Note Payable
During the period:
Average balance		$ 1,300,000,000	$ 1,300,000,000
Weighted-average interest rate (as a percent)		2.88%	4.43%
Total interest expense		$ 9,888,000	$ 14,846,000
Carrying value:
Unpaid principal balance		1,300,000,000		1,300,000,000
Unamortized debt issuance costs		(3,715,000)		(4,160,000)
Notes payable		$ 1,296,285,000		$ 1,295,840,000
Weighted-average interest rate (as a percent)		2.87%		2.93%
Amortization of Financing Costs		$ 544,000	$ 445,000
Note Payable | Credit Suisse AG
Long-Term debt
Maximum loan amount					$ 600,000,000
Note Payable | Mortgage servicing rights
Carrying value:
Assets pledged to secure		3,047,056,000		$ 2,421,326,000
Notes payable
Increase in loan amount		0		0
Note Payable | Servicing advances
Carrying value:
Assets pledged to secure		373,110,000		413,484,000
Note Payable | Deposits
Carrying value:
Assets pledged to secure		$ 102,270,000		153,054,000
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
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
Interest rate spread		2.65%
Unsecured Senior Note
During the period:
Average balance		$ 1,003,889,000
Weighted-average interest rate (as a percent)		4.91%
Total interest expense		$ 12,670,000
Unpaid principal balance		1,300,000,000		650,000,000
Unamortized debt issuance costs and premiums		(11,802,000)		(4,180,000)
Debt Instrument Unamortized Premium And Debt Issuance Costs Net		$ 1,288,198,000		$ 645,820,000
Weighted average interest rate (as a percent)		4.81%		5.38%
Carrying value:
Amortization of Financing Costs		$ 347,000
Notes payable
Maximum loan amount		$ 1,300,000,000
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%	104.25%
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	40.00%
Unsecured Senior Notes One Due October 2025
Notes payable
Maximum loan amount		$ 500,000,000
Interest rate spread		5.38%
Unsecured Senior Notes Two Due October 2025
Notes payable
Maximum loan amount		$ 150,000,000
Interest rate spread		5.38%
Unsecured Senior Notes Due February 2029
Notes payable
Maximum loan amount		$ 650,000,000
Interest rate spread		4.25%