Document and Entity Information	0 Months Ended
	Dec. 31, 2012
Risk/Return:
Document Type	485BPOS
Document Period End Date	Dec. 31, 2012
Registrant Name	SEI INSTITUTIONAL INVESTMENTS TRUST
Central Index Key	0000939934
Amendment Flag	false
Document Creation Date	Apr. 30, 2013
Document Effective Date	Apr. 30, 2013
Prospectus Date	Apr. 30, 2013
SIIT Dynamic Asset Allocation Fund | SIIT Dynamic Asset Allocation Fund - Class A
Risk/Return:
Trading Symbol	SDLAX
SIIT Multi-Asset Real Return Fund | SIIT Multi-Asset Real Return Fund - Class A
Risk/Return:
Trading Symbol	SEIAX