Document and Entity Information Document (USD $)	12 Months Ended
	Dec. 31, 2011	Feb. 23, 2012	Jun. 30, 2011
Entity Information [Line Items]
Entity Registrant Name	AMERISTAR CASINOS INC
Entity Central Index Key	0000912145
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	Q4
Amendment Flag	false
Entity Common Stock, Shares Outstanding		32,867,902
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 756,013,765