Change in Accumulated Balance of Component of Other Comprehensive Loss (Details Textual) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2010
Change in Accumulated Balance of Component of Other Comprehensive Gain Loss (Textual) [Abstract]
Accumulated Other Comprehensive Income Unrealized Holding Gain Loss On Securities Net Of Tax	$ 0	$ 0	$ 13

Accumulated other comprehensive income unrealized holding gain (loss) on securities net of tax.

No definition available.

Name:	idra_AccumulatedOtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesNetOfTax
Namespace Prefix:	idra_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant