Guarantees - Additional Information (Detail)	Aug. 31, 2018 USD ($)
Stand-by Letters of Credit
Guarantor Obligations [Line Items]
Letter of credit amount outstanding	$ 13,912,000
Drawn amount of letter of credit outstanding	0
Operating Lease of Aircraft
Guarantor Obligations [Line Items]
Maximum potential obligation	$ 8,118,000

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=115931803&loc=d3e12069-110248

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