Document and Entity Information - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Oct. 31, 2015	Jun. 30, 2015
Document and Entity Information [Abstract]
Entity Registrant Name	AMBASE CORP
Entity Central Index Key	0000020639
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Smaller Reporting Company
Entity Public Float			$ 62
Entity Common Stock, Shares Outstanding		40,737,751
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2015