Note 4 - Revenue Recognition - Revenues by Revenue Class (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018
Sales by product	$ 36,667	$ 32,325	$ 60,943	$ 61,214
Sales by product	100.00%	100.00%	100.00%	100.00%
Product [Member] | Transferred at Point in Time [Member]
Sales by product	$ 5,860	$ 2,578	$ 10,757	$ 5,007
Sales by product	16.00%	8.00%	18.00%	8.00%
Specialty Piping Systems And Coating [Member] | Transferred at Point in Time Using Input Method [Member]
Sales by product	$ 15,451	$ 9,807	$ 24,238	$ 20,909
Sales by product	42.00%	30.00%	40.00%	34.00%
Specialty Piping Systems And Coating [Member] | Transferred at Point in Time Using Output Method [Member]
Sales by product	$ 15,356	$ 19,940	$ 25,948	$ 35,298
Sales by product	42.00%	62.00%	42.00%	58.00%