Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Oct. 30, 2019
Cover page.    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Sep. 30, 2019  
Document Transition Report false  
Entity File Number 001-33961  
Entity Registrant Name HILL INTERNATIONAL, INC.  
Entity Central Index Key 0001287808  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Amendment Flag false  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 20-0953973  
Entity Address, Address Line One One Commerce Square  
Entity Address, Address Line Two 2005 Market Street, 17th Floor  
Entity Address, City or Town Philadelphia  
Entity Address, State or Province PA  
Entity Address, Postal Zip Code 19103  
City Area Code 215  
Local Phone Number 309-7700  
Title of 12(b) Security Common Stock, par value $0.0001  
Trading Symbol HIL  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   56,161,783