QUARTERLY FINANCIAL INFORMATION (unaudited) - Schedule of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
QUARTERLY FINANCIAL INFORMATION (unaudited)
Revenues	$ 206,760	$ 175,444	$ 162,495	$ 130,348	$ 116,386	$ 113,967	$ 97,434	$ 85,488	$ 675,047	$ 413,275	$ 383,110
Gross profit	37,819	36,578	44,012	28,302	23,543	26,262	28,493	21,167	146,711	99,465	83,603
Income from operations	29,770	26,730	34,499	21,255	14,461	20,672	23,645	15,627	112,254	74,405	64,133
Net income	20,781	19,226	23,299	14,120	9,160	14,359	15,834	10,851	77,426	50,204	43,455
Net income attributable to the stockholders of Argan, Inc.	$ 20,351	$ 18,073	$ 19,674	$ 12,230	$ 6,728	$ 10,807	$ 11,307	$ 7,503	$ 70,328	$ 36,345	$ 30,445
Earnings per share
Basic (in Dollars per share)	$ 1.33	$ 1.19	$ 1.32	$ 0.82	$ 0.45	$ 0.73	$ 0.77	$ 0.51	$ 4.67	$ 2.46	$ 2.11
Diluted (in Dollars per share)	$ 1.29	$ 1.16	$ 1.29	$ 0.81	$ 0.45	$ 0.72	$ 0.75	$ 0.50	$ 4.50	$ 2.42	$ 2.05