Note 7 - Plant Restructuring (Details Textual) - Closing of Northwest Plant [Member] - USD ($)	6 Months Ended	12 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Mar. 31, 2016
Restructuring Charges	$ 57,000		$ 10,302,000
Restructuring Reserve, Accrual Adjustment		$ 1,829,000
Employee Severance [Member]
Restructuring Charges			162,000
Restructuring Reserve, Accrual Adjustment		1,578,000
Impairment of Long-Lived Assets [Member]
Restructuring Charges			5,065,000
Restructuring Reserve, Accrual Adjustment		(384,000)
Other Restructuring [Member]
Restructuring Charges			$ 5,075,000
Restructuring Reserve, Accrual Adjustment		$ 635,000