Investment Securities - Additional Information (Details) $ in Thousands	3 Months Ended	6 Months Ended
Nov. 30, 2021 USD ($) counterparty	Nov. 30, 2020 USD ($)	Nov. 30, 2021 USD ($) counterparty	Nov. 30, 2020 USD ($)	May 31, 2021 USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Unrealized loss	$ 6,000	$ 2,000	$ 9,000
Unrealized gains				$ 1,000
Proceeds for sale of debt investment securities	$ 0	3,000	2,000	6,000
Realized gains		1,000	$ 1,000	1,000
Master repurchase agreements, number of counterparties \| counterparty	2		2
Short-term borrowings	$ 4,746,935		$ 4,746,935		$ 4,582,096
Debt securities trading, at fair value, pledged as collateral	264,932		264,932		210,894
Unrealized gain	2,000	$ 1,000	2,000	$ 2,000
Securities sold under agreements to repurchase
Debt and Equity Securities, FV-NI [Line Items]
Short-term borrowings	$ 249,291		$ 249,291		$ 200,115

Master Repurchase Agreements, Number of Counterparties

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- Definition

Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
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Amount of unrealized gain on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Amount of unrealized loss on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Amount of unrealized gain on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

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The cash inflow associated with the sale of securities classified as trading securities and held for investment purposes. Excludes proceeds from trading securities purchased and held principally for the purpose of selling them in the near term (thus held for only a short period of time).

+ References

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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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Fair value of securities pledged as collateral against securities sold under agreement to repurchase.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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