Document and Entity Information (USD $)	6 Months Ended
	Jun. 30, 2013
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	$ 21,523,000
Entity Common Stock, Shares Outstanding	25,321,000
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q2
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2013