Securitized Mortgage Trusts - Change in Fair Value of Net Trust Assets (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Change in fair value of net trust assets, including trust REO losses
Change in fair value of net trust assets, excluding REO	$ (666)	$ (4,479)	$ (3,190)	$ (1,906)
Gains from REO	(649)	2,734	(46)	8,484
Change in fair value of net trust assets, including trust REO gains	$ (1,315)	$ (1,745)	$ (3,236)	$ 6,578

This element represents change in fair value of trust assets including gain or loss on real estate owned due to increases or decreases in the fair value of investment securities-for-sale, securitized mortgage collateral and securitized mortgage borrowings during the reporting period.

No definition available.

Name:	imh_TrustAssetsNetChangeInFairValueIncludingRealEstateOwnedGainLoss
Namespace Prefix:	imh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration