Borrowings - Assets Sold Under Agreement to Repurchase (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
During the period:
Total interest expense	$ 19,429	$ 4,676	$ 47,709	$ 15,943
Carrying value:
Unpaid principal balance	3,539,459		3,539,459
Unamortized debt issuance costs and premiums	(570)		(570)		$ (1,341)
Total loans sold under agreements to repurchase	3,538,889		3,538,889		1,933,859
Servicing advances	181,747		181,747		162,895
Assets sold under agreements to repurchase
During the period:
Average balance of mortgage loans sold under agreements to repurchase	$ 2,098,208	$ 1,563,053	$ 1,861,086	$ 1,618,008
Weighted-average interest rate (as a percent)	3.66%	3.91%	4.08%	3.72%
Total interest expense	$ 19,429	$ 4,676	$ 47,709	$ 15,943
Maximum daily amount outstanding	3,539,459	2,201,880	3,539,459	2,380,121
Carrying value:
Unpaid principal balance	3,539,459		3,539,459		1,935,200
Unamortized debt issuance costs and premiums	(570)		(570)		(1,341)
Total loans sold under agreements to repurchase	$ 3,538,889		$ 3,538,889		$ 1,933,859
Weighted average interest rate (as a percent)	3.53%		3.53%		4.22%
Available borrowing capacity committed	$ 2,665		$ 2,665		$ 695,767
Available borrowing capacity uncommitted	1,292,876		1,292,876		2,354,033
Available borrowing capacity	1,295,541		1,295,541		3,049,800
Margin deposits placed with counterparties	5,000		5,000		3,750
Amortization of premium	200	10,900	9,200	29,700
Amount of Master Repurchase Agreement incentives to refinance include in interest expense	1,600	$ 12,800	14,700	$ 35,500
Assets sold under agreements to repurchase \| Loans held for sale
Carrying value:
Fair value of assets pledged to secure	3,939,161		3,939,161		1,923,857
Assets sold under agreements to repurchase \| Mortgage servicing rights
Carrying value:
Fair value of assets pledged to secure	2,532,369		2,532,369		2,807,333
Assets sold under agreements to repurchase \| Servicing advances
Carrying value:
Fair value of assets pledged to secure	181,747		181,747		162,895
Assets sold under agreements to repurchase \| Financing receivable
Carrying value:
Fair value of assets pledged to secure	$ 107,678		$ 107,678		$ 131,025

Amount of Master Repurchase Agreement incentives to refinance.

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Unpaid principal balance of assets sold under agreements to repurchase.

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Committed amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Uncommitted amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Aggregate amount of servicing advances pledged to creditors.

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Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

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Amount of unamortized debt discount (premium) and debt issuance costs.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer.

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The sum of the fair values, as of the date of each statement of financial position presented, of securities that are restricted as collateral for the payment of related debt obligations, primarily secured borrowings and repurchase agreements, and that are reclassified and separately reported in the statement of financial position because the transferee has the right by contract or custom to sell or re-pledge them.

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This is the amount of interest expense incurred during the reporting period as a result of repurchase agreements.

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Weighted average interest rate of short-term debt outstanding calculated at point in time.

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Weighted average interest rate of short-term debt outstanding calculated over time.

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For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

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For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, the maximum amount borrowed at any time during the period.

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