Mortgage Servicing (Details) - MSRs	9 Months Ended	12 Months Ended
Sep. 30, 2017 USD ($) Institution	Dec. 31, 2016 USD ($)
Mortgage Servicing
Unpaid principal balance of loans serviced	$ 15,601,225,516	$ 13,555,085,518
Weighted average servicing fee (as a percent)	0.48%	0.478%
Number of federally insured depository institutions holding cash balance and related escrow liabilities for servicing mortgage \| Institution	2
Fee-based servicing portfolio
Mortgage Servicing
Percentage of Total	100.00%	100.00%
Escrow Deposit	$ 506,600,000	$ 401,700,000
Fee-based servicing portfolio \| Texas
Mortgage Servicing
Percentage of Total	23.00%	24.00%
Fee-based servicing portfolio \| North Carolina
Mortgage Servicing
Percentage of Total	10.00%	9.00%
Fee-based servicing portfolio \| California
Mortgage Servicing
Percentage of Total	8.00%	8.00%
Fee-based servicing portfolio \| New York
Mortgage Servicing
Percentage of Total	8.00%	8.00%
Fee-based servicing portfolio \| Georgia
Mortgage Servicing
Percentage of Total	6.00%	5.00%
Fee-based servicing portfolio \| Florida
Mortgage Servicing
Percentage of Total	5.00%
Fee-based servicing portfolio \| Other
Mortgage Servicing
Percentage of Total	40.00%	46.00%
Fannie Mae
Mortgage Servicing
Unpaid principal balance of loans serviced	$ 12,331,135,405	$ 11,181,152,400
Fannie Mae \| Fee-based servicing portfolio
Mortgage Servicing
Percentage of Total	79.00%	83.00%
Freddie Mac
Mortgage Servicing
Unpaid principal balance of loans serviced	$ 2,732,536,579	$ 1,953,244,541
Freddie Mac \| Fee-based servicing portfolio
Mortgage Servicing
Percentage of Total	18.00%	14.00%
FHA
Mortgage Servicing
Unpaid principal balance of loans serviced	$ 537,553,532	$ 420,688,577
FHA \| Fee-based servicing portfolio
Mortgage Servicing
Percentage of Total	3.00%	3.00%

Percentage of servicing fee on loans.

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- Definition

Number of federally insured depository institutions.

+ References

No definition available.

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- Definition

The percentage of unpaid principal balance to total unpaid principal balance as of the balance sheet date.

+ References

No definition available.

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- References

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- Definition

The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

This is the result of the principal amount outstanding of total loans managed or securitized less securitized loans and loans that are in the process of being securitized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719

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