Cover Page - shares	3 Months Ended
	Mar. 31, 2020	May 01, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	0-21220
Entity Registrant Name	ALAMO GROUP INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	74-1621248
Entity Address, Address Line One	1627 East Walnut
Entity Address, City or Town	Seguin
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	78155
City Area Code	830
Local Phone Number	379-1480
Title of 12(b) Security	Common Stock, par value$.10 per share
Trading Symbol	ALG
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		11,860,233
Entity Central Index Key	0000897077
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false