Contract Assets (Details) - USD ($)	Sep. 30, 2018	Mar. 31, 2018
Short-term contract assets [Abstract]
Cores expected to be returned by customers	$ 16,775,000	$ 15,614,000
Upfront payments to customers	3,441,000	3,979,000
Core premiums paid to customers	4,056,000	3,613,000
Total short-term contract assets	24,272,000	23,206,000
Long-term contract assets [Abstract]
Remanufactured cores held at customers' locations	204,692,000	197,067,000
Upfront payments to customers	4,050,000	5,492,000
Core premiums paid to customers	16,127,000	14,603,000
Long-term core inventory deposits	5,569,000	5,569,000
Total long-term contract assets	230,438,000	222,731,000
Total contract assets	$ 254,710,000	$ 245,937,000