Fair Value Measurements - Assumptions used in MSRs and MSRs secured liability (Details)	6 Months Ended	12 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
MSRs Secured Liability
Significant assumptions used in estimating fair value
Weighted-average prepayment speed (CPR)	9.90%		11.20%
Option adjusted spread	8.61%		9.28%
Weighted-average delinquency rate	4.00%		4.00%
MSRs Owned
Significant assumptions used in estimating fair value
Initial capitalization rate of additions to MSRs owned	1.12%	1.14%
Capitalization servicing rate	0.65%		0.67%
Capitalization servicing multiple	220.00%		230.00%
Weighted-average servicing fee (in basis points)	0.29%		0.29%
Weighted-average life (years)	4 years 7 months 30 days		5 years 7 months 30 days
MSRs Owned \| Mortgage servicing rights
Significant assumptions used in estimating fair value
Weighted-average prepayment speed (CPR)	13.20%		9.20%
Option adjusted spread	7.36%		3.93%
Weighted-average delinquency rate	11.80%		12.40%
MSRs Under Secured Borrowing Arrangement
Significant assumptions used in estimating fair value
Capitalization servicing rate	0.95%		0.85%
Capitalization servicing multiple	360.00%		320.00%
Weighted-average servicing fee (in basis points)	0.27%		0.27%
Weighted-average life (years)	5 years 11 months		5 years 7 months
MSRs Under Secured Borrowing Arrangement \| Mortgage servicing rights
Significant assumptions used in estimating fair value
Weighted-average prepayment speed (CPR)	9.90%		11.20%
Option adjusted spread	8.61%		9.28%
Weighted-average delinquency rate	4.00%		4.00%

The weighted average delinquency rate for servicing assets or liabilities.

No definition available.

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- Definition

Represents the capitalization multiple used to estimate the fair value of servicing assets and servicing liabilities.

+ References

No definition available.

+ Details

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- Definition

Represents the initial capitalization rate for additions to servicing assets and servicing liabilities.

+ References

No definition available.

+ Details

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- Definition

Represents the weighted-average servicing fee for servicing assets and servicing liabilities.

+ References

No definition available.

+ Details

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- Definition

Represents the capitalization rate used to estimate the fair value of servicing assets and servicing liabilities.

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Discount rate which is used to value residual cash flows generated by financial assets of a securitization, asset-backed financing arrangement, or similar transfer regardless of when the transfer occurred.

+ 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 (b)(1)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719

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- Definition

Estimated rate of prepayment of principal on financial assets regardless of when the transfer occurred.

+ 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 (b)(2)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719

+ Details

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- Definition

Weighted average life of financial assets and financial liabilities, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122596-111746

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