Notes Payable and Long-Term Debt - Summary of Outstanding Debt Obligations (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Dec. 01, 2019	Nov. 30, 2019
Debt Instrument [Line Items]
Total notes payable and long-term debt, gross	$ 55,971	$ 43,583
Less: unamortized discount and deferred financing costs related to Société Générale 2017 Term Loan Facility	(573)	(641)
Notes payable and long-term debt	55,398	42,942
Current portion of notes payable	2,014	1,972
Current portion of unamortized debt discount and deferred financing costs	(186)	(180)
Current maturities of notes payable and long-term debt	1,828	1,792
Notes payable and long-term debt, net of current maturities	$ 53,570	$ 41,150
Hill International, Inc. - Société Générale 2017 Term Loan Facility | Secured Debt
Debt Instrument [Line Items]
Variable interest rate	7.79%	7.92%
Total notes payable and long-term debt, gross	$ 29,100	$ 29,250
Hill International, Inc. - Société Générale Domestic Revolving Credit Facility | Secured Debt
Debt Instrument [Line Items]
Variable interest rate	5.92%	6.27%
Total notes payable and long-term debt, gross	$ 20,400	$ 9,400
Hill International N.V.. - Société Générale International Revolving Credit Facility | Secured Debt
Debt Instrument [Line Items]
Variable interest rate	4.13%	4.16%
Total notes payable and long-term debt, gross	$ 2,865	$ 2,302
Hill International, Inc. - First Abu Dhabi Bank (FAB) PJSC Overdraft Credit Facility | Unsecured Debt
Debt Instrument [Line Items]
Variable interest rate	5.76%	5.81%
Total notes payable and long-term debt, gross	$ 1,070	$ 593
Hill International Brasil S.A. - Revolving Credit Facility | Unsecured Debt
Debt Instrument [Line Items]
Fixed interest rate	2.80%	3.24%	2.80%	3.30%
Total notes payable and long-term debt, gross	$ 0	$ 498
Hill International Spain SA - Bankia, S.A. and Bankinter, S.A | Unsecured Debt
Debt Instrument [Line Items]
Fixed interest rate	2.21%	2.21%
Total notes payable and long-term debt, gross	$ 795	$ 1,054
Philadelphia Industrial Development Corporation Loan | Unsecured Debt
Debt Instrument [Line Items]
Fixed interest rate	2.79%	2.79%
Total notes payable and long-term debt, gross	$ 451	$ 486
Hill International Spain S.A. - Bankinter S.A. 2020 Term Loan | Unsecured Debt
Debt Instrument [Line Items]
Fixed interest rate	2.23%
Total notes payable and long-term debt, gross	$ 337	0
Hill International Spain S.A. - Banco Santander, S.A. Term Loan | Unsecured Debt
Debt Instrument [Line Items]
Fixed interest rate	3.91%
Total notes payable and long-term debt, gross	$ 337	0
Hill International Spain S.A. - BBVA, S.A. P.P. Term Loan | Unsecured Debt
Debt Instrument [Line Items]
Fixed interest rate	2.28%
Total notes payable and long-term debt, gross	$ 337	0
Hill International Spain S.A. - Bankia. S.A. 2020 Term Loan | Unsecured Debt
Debt Instrument [Line Items]
Fixed interest rate	2.54%
Total notes payable and long-term debt, gross	$ 279	$ 0