Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Jul. 31, 2020
Cover [Abstract]
Entity Registrant Name	AMBASE CORP
Entity Central Index Key	0000020639
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		40,737,751
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Entity Address, State or Province	FL