Long-Term Debt - Note Payable (Details) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
During the period:
Unpaid principal balance	$ 3,336,577,000
Unamortized debt issuance costs and premiums	(3,133,000)		$ (4,625,000)
Carrying value:
Notes payable	1,298,067,000		1,297,622,000
Unsecured senior notes	1,777,132,000		1,776,219,000
Note Payable
During the period:
Average balance	$ 1,300,000,000	$ 1,300,000,000
Weighted-average interest rate (as a percent)	2.95%	2.88%
Total interest expense	$ 9,909,000	$ 9,888,000
Carrying value:
Unpaid principal balance	1,300,000,000		1,300,000,000
Unamortized debt issuance costs	(1,933,000)		(2,378,000)
Notes payable	$ 1,298,067,000		$ 1,297,622,000
Weighted-average interest rate (as a percent)	3.21%		2.84%
Amortization of Financing Costs	$ 459,000	544,000
Notes payable
Maximum loan amount	1,300,000,000
Note Payable | Mortgage servicing rights
Carrying value:
Assets pledged to secure	4,246,586,000		$ 3,856,791,000
Note Payable | Servicing advances
Carrying value:
Assets pledged to secure	230,395,000		232,107,000
Note Payable | Deposits
Carrying value:
Assets pledged to secure	$ 36,106,000		36,632,000
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	$ 1,800,000,000	$ 1,003,889,000
Weighted-average interest rate (as a percent)	5.07%	4.91%
Total interest expense	$ 23,428,000	$ 12,670,000
Unpaid principal balance	1,800,000,000		1,800,000,000
Unamortized debt issuance costs and premiums	(22,868,000)		(23,781,000)
Debt Instrument Unamortized Premium And Debt Issuance Costs Net	$ 1,777,132,000		$ 1,776,219,000
Weighted average interest rate (as a percent)	5.07%		5.07%
Carrying value:
Amortization of Financing Costs	$ 913,000	$ 347,000
Notes payable
Maximum loan amount	$ 1,800,000,000
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)	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%
Unsecured Senior Notes Due September 2031
Notes payable
Maximum loan amount	$ 500,000,000
Interest rate spread	5.75%