Inventory (Details) - USD ($)		Sep. 30, 2018	Mar. 31, 2018
Inventory [Abstract]
Raw materials		$ 89,919,000	$ 77,135,000
Work-in-process		3,811,000	2,583,000
Finished goods		104,584,000	88,174,000
Inventory, gross		198,314,000	167,892,000
Less allowance for excess and obsolete inventory		(10,027,000)	(6,682,000)
Total inventory - net		188,287,000	161,210,000
Inventory unreturned		$ 9,100,000	7,508,000
Long-term core inventory [Abstract]
Used cores held at the Company's facilities			0
Used cores expected to be returned by customers			0
Remanufactured cores held in finished goods			0
Remanufactured cores held at customers' locations			0
Long-term core inventory - gross			0
Less allowance for excess and obsolete inventory			0
Total			0
Long-term core inventory deposits			0
As Revised [Member] | ASC 606 [Member]
Inventory [Abstract]
Raw materials			25,805,000
Work-in-process			635,000
Finished goods			53,973,000
Inventory, gross			80,413,000
Less allowance for excess and obsolete inventory			(4,138,000)
Total inventory - net			76,275,000
Inventory unreturned			7,508,000
Long-term core inventory [Abstract]
Used cores held at the Company's facilities			53,278,000
Used cores expected to be returned by customers			12,970,000
Remanufactured cores held in finished goods			34,201,000
Remanufactured cores held at customers' locations			200,389,000
Long-term core inventory - gross			300,838,000
Less allowance for excess and obsolete inventory			(2,544,000)
Total			298,294,000
Long-term core inventory deposits			5,569,000
Adoption of ASC 2014-09 [Member] | ASC 606 [Member]
Inventory [Abstract]
Raw materials	[1]		51,330,000
Work-in-process	[1]		1,948,000
Finished goods	[2]		34,201,000
Inventory, gross			87,479,000
Less allowance for excess and obsolete inventory	[3]		(2,544,000)
Total inventory - net			84,935,000
Inventory unreturned			0
Long-term core inventory [Abstract]
Used cores held at the Company's facilities	[1]		(53,278,000)
Used cores expected to be returned by customers	[4]		(12,970,000)
Remanufactured cores held in finished goods	[2]		(34,201,000)
Remanufactured cores held at customers' locations	[5]		(200,389,000)
Long-term core inventory - gross			(300,838,000)
Less allowance for excess and obsolete inventory	[3]		2,544,000
Total			(298,294,000)
Long-term core inventory deposits	[6]		$ (5,569,000)

[1] Used cores held at the Company's facilities of $53,278,000 have been reclassified to raw materials and work-in-process in the consolidated balance sheet at March 31, 2018.

[2] Remanufactured Cores held in finished goods of $34,201,000 have been reclassified to finished goods in the consolidated balance sheet at March 31, 2018.

[3] The allowance for excess and obsolete inventory of $2,544,000 previously included in long-term core inventory has been reclassified to inventory-net in the consolidated balance sheet at March 31, 2018.

[4] Used cores expected to be returned by customers of $12,970,000 have been reclassified to contract assets in the consolidated balance sheet at March 31, 2018.

[5] Remanufactured cores held at customers' locations of $200,389,000 have been reclassified to current and long-term contract assets in the consolidated balance sheet at March 31, 2018.

[6] Long-term core inventory deposits of $5,569,000 have been reclassified to long-term contract assets in the consolidated balance sheet at March 31, 2018.