Derivative Transactions - Schedule of Cash Settlements and Net Losses and Net (Gains) on Mark-to-Market Adjustments for Changes in Fair Value of Derivative Contracts (Detail) - USD ($) $ in Thousands	3 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Derivatives, Fair Value [Line Items]
Total net unrealized mark-to-market loss (gains)	$ 1,788	$ (625)
Total net realized gains	(159)	(384)
Diesel Fuel Option Collars [Member]
Derivatives, Fair Value [Line Items]
Total net unrealized mark-to-market loss (gains)	69	(12)
Total net realized gains	7	(308)
Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Total net unrealized mark-to-market loss (gains)	1,726	(613)
Total net realized gains	(166)	(25)
Foreign Exchange Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Total net unrealized mark-to-market loss (gains)	$ (7)
Total net realized gains		$ (51)

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.3(a))
-URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of open derivatives, commodity, or energy contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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