Fair Value of Financial Instruments - Valuation Techniques And Unobservable Inputs Applied (Details) - Level 3	Mar. 31, 2020 USD ($)
Securitized mortgage borrowings \| DCF
Valuation techniques
Estimated fair value of liabilities	$ (2,238,208,000)
Securitized mortgage borrowings \| Measurement Input, Default Rate \| DCF \| Minimum
Unobservable input
Measurement input, securitized mortgage borrowings	0.02
Securitized mortgage borrowings \| Measurement Input, Default Rate \| DCF \| Maximum
Unobservable input
Measurement input, securitized mortgage borrowings	24.0
Securitized mortgage borrowings \| Measurement Input, Default Rate \| DCF \| Weighted Average
Unobservable input
Measurement input, securitized mortgage borrowings	2.4
Securitized mortgage borrowings \| Measurement Input, Loss Severity \| DCF \| Minimum
Unobservable input
Measurement input, securitized mortgage borrowings	6.3
Securitized mortgage borrowings \| Measurement Input, Loss Severity \| DCF \| Maximum
Unobservable input
Measurement input, securitized mortgage borrowings	91.7
Securitized mortgage borrowings \| Measurement Input, Loss Severity \| DCF \| Weighted Average
Unobservable input
Measurement input, securitized mortgage borrowings	56.8
Securitized mortgage borrowings \| Measurement Input, Discount Rate \| DCF \| Minimum
Unobservable input
Measurement input, securitized mortgage borrowings	4.4
Securitized mortgage borrowings \| Measurement Input, Discount Rate \| DCF \| Maximum
Unobservable input
Measurement input, securitized mortgage borrowings	25.0
Securitized mortgage borrowings \| Measurement Input, Discount Rate \| DCF \| Weighted Average
Unobservable input
Measurement input, securitized mortgage borrowings	5.7
Long-term debt \| DCF
Valuation techniques
Estimated fair value of liabilities	$ (39,632,000)
Long-term debt \| Measurement Input, Discount Rate \| DCF
Unobservable input
Measurement input, long-term debt	9.0
Long-term debt \| Measurement Input, Discount Rate \| DCF \| Weighted Average
Unobservable input
Measurement input, long-term debt	9.0
Securitized mortgage collateral \| DCF
Valuation techniques
Estimated fair value of assets	$ 2,248,813,000
Securitized mortgage collateral \| Measurement Input, Prepayment Rate \| DCF \| Minimum
Unobservable input
Measurement input, securitized mortgage collateral	2.5
Securitized mortgage collateral \| Measurement Input, Prepayment Rate \| DCF \| Maximum
Unobservable input
Measurement input, securitized mortgage collateral	34.6
Securitized mortgage collateral \| Measurement Input, Prepayment Rate \| DCF \| Weighted Average
Unobservable input
Measurement input, securitized mortgage collateral	8.4
Mortgage servicing rights \| DCF
Valuation techniques
Estimated fair value of assets	$ 24,328,000
Mortgage servicing rights \| Measurement Input, Prepayment Rate \| DCF \| Minimum
Unobservable input
Measurement input, mortgage servicing rights	8.1
Mortgage servicing rights \| Measurement Input, Prepayment Rate \| DCF \| Maximum
Unobservable input
Measurement input, mortgage servicing rights	88.8
Mortgage servicing rights \| Measurement Input, Prepayment Rate \| DCF \| Weighted Average
Unobservable input
Measurement input, mortgage servicing rights	24.8
Mortgage servicing rights \| Measurement Input, Discount Rate \| DCF \| Minimum
Unobservable input
Measurement input, mortgage servicing rights	9.0
Mortgage servicing rights \| Measurement Input, Discount Rate \| DCF \| Maximum
Unobservable input
Measurement input, mortgage servicing rights	13.0
Mortgage servicing rights \| Measurement Input, Discount Rate \| DCF \| Weighted Average
Unobservable input
Measurement input, mortgage servicing rights	9.2
Interest rate lock commitments. net (IRLCs) \| Market pricing
Valuation techniques
Estimated fair value of assets	$ 863,000
Interest rate lock commitments. net (IRLCs) \| Measurement Input, Pull-through Rate \| Market pricing \| Minimum
Unobservable input
Measurement input, derivative assets - IRLCs, net	0.0
Interest rate lock commitments. net (IRLCs) \| Measurement Input, Pull-through Rate \| Market pricing \| Maximum
Unobservable input
Measurement input, derivative assets - IRLCs, net	99.9
Interest rate lock commitments. net (IRLCs) \| Measurement Input, Pull-through Rate \| Market pricing \| Weighted Average
Unobservable input
Measurement input, derivative assets - IRLCs, net	6.0

No definition available.

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

- Definition

Value of input used to measure securitized mortgage collateral.

+ References

No definition available.

+ Details

Name:	imh_SecuritizedMortgageCollateralMeasurementInput
Namespace Prefix:	imh_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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

- Definition

Value of input used to measure debt instrument, including, but not limited to, convertible and non-convertible debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_DebtInstrumentMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Value of input used to measure derivative asset.

+ References

+ Details

Name:	us-gaap_DerivativeAssetMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Fair value of financial and nonfinancial obligations.

+ References

+ Details

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

- Definition

Value of input used to measure long-term debt.

+ References

+ Details

Name:	us-gaap_LongTermDebtMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Value of input used to measure servicing asset.

+ References

+ Details

Name:	us-gaap_ServicingAssetMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant