Borrowings - Note Payable (Details) - USD ($)			3 Months Ended
	Aug. 10, 2018	Feb. 28, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Nov. 01, 2018	Feb. 01, 2018
During the period:
Total interest expense			$ 17,995,000	$ 18,222,000
Carrying value:
Notes payable			1,292,736,000		$ 1,292,291,000
Notes payable
Repayments of notes payable				400,000,000
Debt issuance costs				3,400,000
Note Payable
During the period:
Average balance			$ 1,300,000,000	$ 979,868,000
Weighted-average interest rate (as a percent)			5.25%	5.63%
Total interest expense			$ 17,995,000	$ 18,222,000
Maximum daily amount outstanding			1,300,000,000	1,150,000,000
Carrying value:
Unpaid principal balance			1,300,000,000		1,300,000,000
Unamortized issuance costs			(7,264,000)		(7,709,000)
Notes payable			$ 1,292,736,000		$ 1,292,291,000
Weighted-average interest rate (as a percent)			5.24%		5.07%
Unused amount			$ 150,000,000		$ 150,000,000
Amortization of Financing Costs			700,000	4,200,000
Non-utilization fees			196,000	192,000
Notes payable
Debt issuance costs	$ 4,600,000
Note Payable | Revolving credit agreement
Short-term debt
Maximum loan amount						$ 150,000,000
Note Payable | LIBOR
Notes payable
Maximum loan amount	$ 650,000,000	$ 650,000,000
Description of variable rate	one-month LIBOR	one-month LIBOR
Interest rate spread	2.65%	2.85%
Note Payable | Credit Suisse AG
Short-term debt
Maximum loan amount							$ 400,000,000
Note Payable | Mortgage servicing rights
Carrying value:
Assets pledged to secure			2,675,704,000		2,807,333,000
Note Payable | Cash.
Carrying value:
Assets pledged to secure			93,372,000		108,174,000
Note Payable | Servicing advances
Carrying value:
Assets pledged to secure			147,435,000		162,895,000
Mortgage Loan Participation and Sale Agreement member
During the period:
Average balance			236,667,000	215,614,000
Carrying value:
Unamortized issuance costs			(159,000)		$ (215,000)
Amortization of Financing Costs			$ 135,000	$ 171,000