Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Jul. 31, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2021
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity Registrant Name	GSE Systems, Inc.
Entity Incorporation, State or Country Code	DE
Entity File Number	001-14785
Entity Tax Identification Number	52-1868008
Entity Address, Address Line One	1332 LONDONTOWN BLVD
Entity Address, City or Town	SYKESVILLE
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	21784
City Area Code	410
Local Phone Number	970-7874
Entity Filer Category	Non-accelerated Filer
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Small Business	true
Entity Common Stock, Shares Outstanding		20,863,518
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Entity Central Index Key	0000944480
Title of 12(b) Security	Common Stock, $0.01 Par Value
Trading Symbol	GVP
Security Exchange Name	NASDAQ