Commitments and Contingencies - Repurchase Reserve Activity (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Continuing operations repurchase reserve activity
Beginning balance	$ 6,020	$ 5,408
Provision for repurchases	5,435	1,557
Settlements	(2,335)	(945)
Total repurchase reserve	9,120	6,020
Approved warehouse lines	1,000,000
Outstanding balance	$ 731	$ 41,777

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

Name:	imh_MovementInMortgageLoansOnRealEstateRepurchaseReserveRollForward
Namespace Prefix:	imh_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the amount reserved for repurchase of loans in the event of a breach in representation or warranty provided to the loan purchaser.

+ References

No definition available.

+ Details

Name:	imh_RepurchaseReserve
Namespace Prefix:	imh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the provision charged for loan repurchases for the period.

+ References

No definition available.

+ Details

Name:	imh_RepurchaseReserveProvision
Namespace Prefix:	imh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the settlement amount for loan repurchases for the period.

+ References

No definition available.

+ Details

Name:	imh_RepurchaseReserveSettlements
Namespace Prefix:	imh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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