Revenue Recognition, Statement of Cash Flows (Details) - USD ($)	3 Months Ended			6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities [Abstract]
Net income	$ 3,513,000	$ 5,595,000	$ 7,820,000	$ (1,982,000)	$ 13,415,000
Deferred income taxes			209,000	(667,000)	(207,000)
Accounts receivable			9,333,000	6,598,000	2,819,000
Inventory			(18,494,000)	(32,380,000)	(28,552,000)
Other assets			(1,000)	(79,000)	(20,000)
Long-term core inventory			0		0
Contract assets, net			1,726,000	(8,773,000)	6,882,000
Contract liabilities, net			3,172,000	2,724,000	5,837,000
Accrued core payments			0		0
Net cash used in operating activities			(644,000)	$ (6,409,000)	(8,148,000)
As Revised [Member] | ASC 606 [Member]
Cash flows from operating activities [Abstract]
Net income		5,723,000	7,295,000		13,018,000
Deferred income taxes			(103,000)		(433,000)
Accounts receivable			16,038,000		14,683,000
Inventory			(14,942,000)		(18,718,000)
Other assets			1,432,000		2,943,000
Long-term core inventory			(2,878,000)		(5,155,000)
Contract assets, net			0		0
Contract liabilities, net			0		0
Accrued core payments			(3,077,000)		(6,164,000)
Net cash used in operating activities			(644,000)		(8,148,000)
Adoption of ASC 606 [Member] | ASC 606 [Member]
Cash flows from operating activities [Abstract]
Net income		$ (128,000)	525,000		397,000
Deferred income taxes			312,000		226,000
Accounts receivable			(6,705,000)		(11,864,000)
Inventory			(3,552,000)		(9,834,000)
Other assets			(1,433,000)		(2,963,000)
Long-term core inventory			2,878,000		5,155,000
Contract assets, net			1,726,000		6,882,000
Contract liabilities, net			3,172,000		5,837,000
Accrued core payments			3,077,000		6,164,000
Net cash used in operating activities			$ 0		$ 0