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Cover Page - $ / shares
 6 Months Ended
Jun. 30, 2021
Jul. 16, 2021
Dec. 31, 2020
Document and Entity Information [Abstract]      
Document Type 10-Q    
Document Quarterly Report true    
Document Period End Date Jun. 30, 2021    
Document Transition Report false    
Entity File Number 001-33166    
Entity Registrant Name Allegiant Travel Co    
Entity Incorporation, State or Country Code NV    
Entity Tax Identification Number 20-4745737    
Entity Address, Address Line One 1201 North Town Center Drive    
Entity Address, City or Town Las Vegas,    
Entity Address, State or Province NV    
Entity Address, Postal Zip Code 89144    
City Area Code 702    
Local Phone Number 851-7300    
Title of 12(b) Security Common stock, par value $0.001    
Trading Symbol ALGT    
Security Exchange Name NASDAQ    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Emerging Growth Company false    
Entity Small Business false    
Entity Shell Company true    
Entity Common Stock, Shares Outstanding   17,986,507  
Current Fiscal Year End Date --12-31    
Amendment Flag false    
Entity Central Index Key 0001362468    
Document Fiscal Year Focus 2021    
Document Fiscal Period Focus Q2    
Common Stock, Par or Stated Value Per Share $ 0.001 $ 0.001 $ 0.001