Allowance for Loan Losses - Additional Information (Details) - USD ($) $ in Thousands	Nov. 30, 2019	May 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Credit reserve for unadvanced loan commitments	$ 1,000	$ 1,000
Nonperforming Financial Instruments
Financing Receivable, Allowance for Credit Loss [Line Items]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	$ 0	$ 0

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953550-111524

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant