Borrowings - Assets Sold Under Agreement to Repurchase (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
During the period:
Total interest expense	$ 4,676	$ 19,203	$ 15,943	$ 52,249
Carrying value:
Unpaid principal balance	1,738,839		1,738,839
Unamortized debt issuance costs and premiums	799		799		$ 672
Total loans sold under agreements to repurchase	1,739,638		1,739,638		2,381,538
Assets sold under agreements to repurchase
During the period:
Average balance of mortgage loans sold under agreements to repurchase	$ 1,563,053	$ 1,960,332	$ 1,618,008	$ 1,854,786
Weighted-average interest rate (as a percent)	3.91%	3.23%	3.72%	3.15%
Total interest expense	$ 4,676	$ 19,203	$ 15,943	$ 52,249
Maximum daily amount outstanding	2,201,880	2,564,756	2,380,121	2,581,199
Carrying value:
Unpaid principal balance	1,738,839		1,738,839		2,380,866
Unamortized debt issuance costs and premiums	799		799		672
Total loans sold under agreements to repurchase	$ 1,739,638		$ 1,739,638		$ 2,381,538
Weighted average interest rate (as a percent)	3.93%		3.93%		3.24%
Available borrowing capacity committed	$ 449,370		$ 449,370		$ 316,503
Available borrowing capacity uncommitted	2,796,791		2,796,791		2,257,631
Available borrowing capacity	3,246,161		3,246,161		2,574,134
Margin deposits placed with counterparties	3,750		3,750		3,750
Amortization of premium	10,900	$ 3,000	29,700	$ 7,900
Amount of Master Repurchase Agreement incentives to refinance include in interest expense	12,800		$ 35,500
Initial term of Master Repurchase Agreement			6 months
Assets sold under agreements to repurchase \| Mortgage Loans held for sale
Carrying value:
Fair value of assets pledged to secure	1,841,097		$ 1,841,097		2,530,299
Assets sold under agreements to repurchase \| Mortgage servicing rights
Carrying value:
Fair value of assets pledged to secure	2,539,575		2,539,575		2,098,067
Assets sold under agreements to repurchase \| Servicing advances
Carrying value:
Fair value of assets pledged to secure	102,222		102,222		114,643
Assets sold under agreements to repurchase \| Financing receivable
Carrying value:
Fair value of assets pledged to secure	$ 133,128		$ 133,128		$ 144,128

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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Represents the initial term of Master Repurchase Agreement.

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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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No definition available.

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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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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration cost.

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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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The average effective interest rate during the reporting period.

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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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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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