Cover Page - shares	6 Months Ended
	Jun. 30, 2020	Aug. 03, 2020
Document and Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
Document Transition Report	false
Entity File Number	001-38098
Entity Registrant Name	APPIAN CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	54-1956084
Entity Address, Address Line One	7950 Jones Branch Drive
Entity Address, City or Town	McLean
Entity Address, State or Province	VA
Entity Address, Postal Zip Code	22102
City Area Code	(703)
Local Phone Number	442-8844
Title of 12(b) Security	Class A Common Stock
Trading Symbol	APPN
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Central Index Key	0001441683
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false
Class A Common Stock
Document and Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		37,632,914
Class B Common Stock
Document and Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		32,217,936