The expense charged against earnings for the periodic recognition of capitalized leases. This element may apply to energy companies that lease mineral producing properties and to other enterprises that capitalize property, plant, or equipment obtained through capital leases.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6455314&loc=d3e45031-112735

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

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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 number of units (items of property) under capital lease arrangements.

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The total gross amount less the charge for the use of the long-lived depreciable assets subject to a lease meeting the criteria for capitalization.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)
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The total charge for the use of long-lived depreciable assets subject to a lease meeting the criteria for capitalization.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6455314&loc=d3e45014-112735

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Commitments and Contingencies - Capital Leases (Details) $ in Thousands	12 Months Ended
	Apr. 30, 2017 USD ($) property	Apr. 30, 2016 USD ($)	Apr. 30, 2015 USD ($)
Capital leases
Carrying value of property and equipment under capital leases	$ 15,018	$ 10,928
Accumulated depreciation on property and equipment under capital leases	8,331	6,696
Depreciation and amortization expense
Capital leases
Amortization of assets held under capital leases	$ 5,310	$ 4,685	$ 4,320
Facility
Capital leases
Number of properties under capital lease \| property	1
Capital lease obligations \| Vehicles \| Minimum
Capital leases
Term	1 year
Capital lease obligations \| Vehicles \| Maximum
Capital leases
Term	5 years
Capital lease obligations \| Facility
Capital leases
Term	11 years