EARNINGS PER SHARE (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net income	$ 18,208	$ 16,354	$ 38,571	$ 28,312
Less: Income attributable to redeemable noncontrolling interest	(212)	0	(527)	0
Net income attributable to CSW Industrials, Inc.	$ 17,996	$ 16,354	$ 38,044	$ 28,312
Weighted average shares:
Common stock (in shares)	15,637	14,651	15,621	14,627
Participating securities (in shares)	118	96	114	100
Denominator for basic earnings per common share (in shares)	15,755	14,747	15,735	14,727
Potentially dilutive securities (in shares)	56	95	61	98
Denominator for diluted earnings per common share (in shares)	15,811	14,842	15,796	14,825
Net income per share attributable to CSW Industrials, Inc. shareholders:
Basic (USD per share)	$ 1.14	$ 1.11	$ 2.42	$ 1.92
Diluted (USD per share)	$ 1.14	$ 1.10	$ 2.41	$ 1.91