Income Taxes - Summary of Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
May 31, 2018	May 31, 2017
Movement in Valuation Allowance [Roll Forward]
Balance at beginning of period	$ (18,088)	$ (17,047)
Additions	(3,268)	(1,667)
Subtractions (1)	10,054	626
Balance at end of period	$ (11,302)	$ (18,088)

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

Name:	us-gaap_DeferredTaxAssetsValuationAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant