Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	May 01, 2017
Document And Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q1
Trading Symbol	CIX
Entity Registrant Name	COMPX INTERNATIONAL INC
Entity Central Index Key	0001049606
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Class A Common Stock
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		2,419,107
Class B Common Stock
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		10,000,000