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Credit Enhancement Receivable, Contingent Liability & Credit Enhancement Deposit - Additional Information (Detail) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017
Credit Enhancement Receivable Contingent Liability And Credit Enhancement Deposit [Line Items] |  |  |
Credit enhancement agreement date | Mar. 09, 2012 |  |
Restricted Cash And Offsetting Liability [Member] |  |  |
Credit Enhancement Receivable Contingent Liability And Credit Enhancement Deposit [Line Items] |  |  |
Deposit in Fannie Mae restricted liquidity account | $ 25,000,000 |  |
Credit Risk [Member] |  |  |
Credit Enhancement Receivable Contingent Liability And Credit Enhancement Deposit [Line Items] |  |  |
Credit risk loans | 18,900,000,000 |  | $ 18,800,000,000
Maximum pre-credit enhancement loss exposure | 5,400,000,000 |  | 5,300,000,000
DB Cayman [Member] |  |  |
Credit Enhancement Receivable Contingent Liability And Credit Enhancement Deposit [Line Items] |  |  |
Reimbursements under serving agreement | 0 | $ 0 |
Credit risk loans | 400,000,000 |  | 4,200,000,000
Maximum pre-credit enhancement loss exposure | 100,000,000 |  | 1,200,000,000
Maximum loss exposure without any form of credit protection | 5,300,000,000 |  | 4,100,000,000
Credit enhancement receivable | $ 0 |  | 10,000
Security deposit return date | Mar. 09, 2021 |  |
Percentage of contingent payment | 50.00% |  |
Contingent payment due date | Mar. 09, 2021 |  |
Contingent payments description | The Company is required to pay DB Cayman on March 9, 2021, an amount equal to 50% of the positive difference, if any, between (a) $25 million, and (b) the Company’s unreimbursed loss sharing payments from March 9, 2012 through March 9, 2021 on the Company’s servicing portfolio as of March 9, 2012. |  |
Contingent liability | $ 10,700,000 |  | $ 10,700,000
DB Entities [Member] |  |  |
Credit Enhancement Receivable Contingent Liability And Credit Enhancement Deposit [Line Items] |  |  |
Deposit in Fannie Mae restricted liquidity account | $ 25,000,000 |  |

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- Definition Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611 + Details
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