Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 25, 2019	Jun. 30, 2018
Document And Entity Information
Entity Registrant Name	AAON INC
Entity Central Index Key	0000824142
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Is Entity a Well-known Seasoned Issuer?	No
Is Entity a Voluntary Filer?	No
Is Entity's Reporting Status Current?	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		51,976,455
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2018
Entity Public Float			$ 1,360.8
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false