Borrowings - Note Payable (Details) - USD ($)					12 Months Ended
	Aug. 10, 2018	Feb. 28, 2018	Aug. 10, 2017	Feb. 16, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Feb. 01, 2018
During the period:
Total interest expense					$ 69,710,000	$ 73,610,000	$ 39,369,000
Carrying value:
Notes payable					1,294,070,000	1,292,291,000
Notes payable
Repayments of notes payable						900,000,000	186,935,000
Note Payable
During the period:
Average balance					$ 1,300,000,000	$ 1,169,452,000	$ 586,135,000
Weighted-average interest rate (as a percent)					5.08%	5.29%	5.86%
Total interest expense					$ 67,789,000	$ 71,697,000	$ 37,001,000
Maximum daily amount outstanding					1,300,000,000	1,300,000,000	900,006,000
Carrying value:
Unpaid principal balance					1,300,000,000	1,300,000,000
Unamortized debt issuance costs					(5,930,000)	(7,709,000)
Notes payable					$ 1,294,070,000	$ 1,292,291,000
Weighted-average interest rate (as a percent)					4.46%	5.07%
Amortization of Financing Costs					$ 1,800,000	$ 9,800,000	$ 3,400,000
Notes payable
Repayments of notes payable	$ 500,000,000	$ 400,000,000
Debt issuance costs					4,600,000
Beneficial interest in mortgage servicing rights					2,800,000,000
Note Payable | Revolving credit agreement
Short-term debt
Maximum loan amount					150,000,000
Carrying value:
Notes payable					0	0
Note Payable | LIBOR
Notes payable
Maximum loan amount	$ 650,000,000	$ 650,000,000	$ 500,000,000	$ 400,000,000
Description of variable rate	one-month LIBOR	one-month LIBOR	one-month LIBOR	one-month LIBOR
Interest rate spread	2.65%	2.85%	4.00%	4.75%
Note Payable | Credit Suisse AG
Short-term debt
Maximum loan amount								$ 400,000,000
Carrying value:
Notes payable					0
Note Payable | Mortgage servicing rights
Carrying value:
Assets pledged to secure					2,861,442,000	2,807,333,000
Note Payable | Servicing advances
Carrying value:
Assets pledged to secure					207,460,000	$ 162,895,000
Loan and Security Agreement
Notes payable
Debt issuance costs					$ 3,400,000