Condensed Parent Company Financial Information - Restricted Net Assets and Dividends (Details) - Consolidated Subsidiaries - USD ($) $ in Thousands	12 Months Ended
Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Condensed Parent Company Financial Information
Restricted net assets	$ 578,000
Cash dividends paid to parent company by consolidated subsidiaries	$ 0	$ 0	$ 0

Amount of restricted net assets of consolidated and unconsolidated subsidiaries as of the end of the most recently completed fiscal year.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e)(3)(ii))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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- Definition

This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(b))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 235
-Section S99
-Paragraph 2
-Subparagraph (SX 210.9-06)
-URI http://asc.fasb.org/extlink&oid=6882215&loc=d3e537971-122884

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- Definition

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.

+ References

No definition available.

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