Percentage of proceeds received upon sale.

No definition available.

Name:	imh_PercentageOfProceedsReceivedUponSale
Namespace Prefix:	imh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of proceeds received upon transfer of all trailing documents.

+ References

No definition available.

+ Details

Name:	imh_PercentageOfProceedsReceivedUponTransferOfAllTrailingDocuments
Namespace Prefix:	imh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of proceeds received upon transfer of servicing.

+ References

No definition available.

+ Details

Name:	imh_PercentageOfProceedsReceivedUponTransferOfServicing
Namespace Prefix:	imh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from the sale of servicing rights, which contractually entitle the servicer to receive fees and ancillary revenues for performing billing, collection, disbursement and recordkeeping services in connection with a mortgage portfolio. Rights may be obtained via (1) acquisition or assumption of a servicing obligation that does not relate to financial assets of the servicer or its consolidated affiliates; or (2) by originating mortgage loans and then (a) transferring the loans to a Variable Interest Entity (VIE) in a transaction that meets the necessary transfer and classification requirements, or (b) transferring the loans in a transaction that meets the requirements for sale accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=7524895&loc=d3e120260-111741

+ Details

Name:	us-gaap_ProceedsFromSaleOfMortgageServicingRightsMSR
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746

+ Details

Name:	us-gaap_ServicingAssetAtFairValueAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Subsequent Events (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
Subsequent Events (Details) - USD ($) $ in Thousands	Oct. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Events
Value of MSRs sold			$ 181,005	$ 154,405	$ 131,537
Proceeds from the sale of mortgage servicing rights		$ 805
Subsequent Event
Subsequent Events
Percentage of proceeds received upon sale	80.00%
Percentage of proceeds received upon transfer of servicing	10.00%
Percentage of proceeds received upon transfer of all trailing documents	10.00%
Subsequent Event \| Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Subsequent Events
Value of MSRs sold	$ 3,400,000
Proceeds from the sale of mortgage servicing rights	$ 35,900